Fix building against Lens 5 by commenting out type signatures(!).

Taken from upstream:

  https://github.com/ganeti/ganeti/commit/5e30bad1bba63c9f6c782003ef2560f107a0ba24

diff --git a/src/Ganeti/Network.hs b/src/Ganeti/Network.hs
index 1cb6aa1ec..696c1cd1b 100644
--- a/src/Ganeti/Network.hs
+++ b/src/Ganeti/Network.hs
@@ -87,11 +87,11 @@ data PoolPart = PoolInstances | PoolExt
 addressPoolIso :: Iso' AddressPool BA.BitArray
 addressPoolIso = iso apReservations AddressPool
 
-poolLens :: PoolPart -> Lens' Network (Maybe AddressPool)
+--poolLens :: PoolPart -> Lens' Network (Maybe AddressPool)
 poolLens PoolInstances = networkReservationsL
 poolLens PoolExt = networkExtReservationsL
 
-poolArrayLens :: PoolPart -> Lens' Network (Maybe BA.BitArray)
+--poolArrayLens :: PoolPart -> Lens' Network (Maybe BA.BitArray)
 poolArrayLens part = poolLens part . mapping addressPoolIso
 
 netIpv4NumHosts :: Network -> Integer
diff --git a/src/Ganeti/Utils/MultiMap.hs b/src/Ganeti/Utils/MultiMap.hs
index d54da3ab0..279e9335a 100644
--- a/src/Ganeti/Utils/MultiMap.hs
+++ b/src/Ganeti/Utils/MultiMap.hs
@@ -91,7 +91,7 @@ multiMap :: (Ord k, Ord v) => M.Map k (S.Set v) -> MultiMap k v
 multiMap = MultiMap . M.filter (not . S.null)
 
 -- | A 'Lens' that allows to access a set under a given key in a multi-map.
-multiMapL :: (Ord k, Ord v) => k -> Lens' (MultiMap k v) (S.Set v)
+--multiMapL :: (Ord k, Ord v) => k -> Lens' (MultiMap k v) (S.Set v)
 multiMapL k f = fmap MultiMap
                  . at k (fmap (mfilter (not . S.null) . Just)
                          . f . fromMaybe S.empty)
-- 
2.41.0

'right' method='get' action='/guix/log/build-aux/hydra/gnu-system.scm'>
<input type='hidden' name='id' value='eb622c6b128024179494253510bebe8bcacb8e6f'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=eb622c6b128024179494253510bebe8bcacb8e6f'>root</a>/<a href='/guix/log/build-aux?id=eb622c6b128024179494253510bebe8bcacb8e6f'>build-aux</a>/<a href='/guix/log/build-aux/hydra?id=eb622c6b128024179494253510bebe8bcacb8e6f'>hydra</a>/<a href='/guix/log/build-aux/hydra/gnu-system.scm?id=eb622c6b128024179494253510bebe8bcacb8e6f'>gnu-system.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/build-aux/hydra/gnu-system.scm?id=eb622c6b128024179494253510bebe8bcacb8e6f&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-03-22 12:42:52 +0100'>2020-03-22</span></td><td><a href='/guix/commit/build-aux/hydra/gnu-system.scm?id=66a198c8075f02d7075a555b48dd3adde88ebbbf'>hydra: evaluate: Use 'with-build-handler'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/hydra/evaluate.scm (command-line): Remove 'set!' for
'build-things'.  Use 'with-build-handler' instead.
* build-aux/hydra/gnu-system.scm (hydra-jobs): Add comment about
removing 'show-what-to-build' call.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-05 23:40:24 +0100'>2020-03-05</span></td><td><a href='/guix/commit/build-aux/hydra/gnu-system.scm?id=530e31b82448ba00dbbe6abc078204d340c09cb1'>hydra: Remove uses of _IOLBF.</a><span class='msg-avail'>...<span class='msg-tooltip'>_IOLBF &amp; co. were deprecated in Guile 2.2 and removed in 3.0.

* build-aux/hydra/gnu-system.scm: Pass 'line instead of _IOLBF to 'setvbuf'.
* build-aux/hydra/guix-modular.scm: Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-12-01 11:26:11 +0100'>2019-12-01</span></td><td><a href='/guix/commit/build-aux/hydra/gnu-system.scm?id=f71b0a0012d46bd30ead1a14ed58fd59647415e2'>ci: Make sure the Guix checkout is the one providing Cuirass proc.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/36378&gt;.
Reported by Reza Alizadeh Majd &lt;r.majd@pantherx.org&gt;.

* build-aux/hydra/gnu-system.scm (find-current-checkout): New procedure.
(hydra-jobs): Use FIND-CURRENT-CHECKOUT to define CHECKOUT.  Pass it to the
inferior Guix as an extra argument whose key is 'superior-guix-checkout'.
* gnu/ci.scm (find-current-checkout): New procedure.
(hydra-jobs): Use FIND-CURRENT-CHECKOUT to define CHECKOUT.  This will return
'#f' if the current Guix is an inferior.  In that case, use the
'superior-guix-checkout' argument provided by the superior Guix.
</span></span></td><td>Clément Lassieur</td></tr>