Don't check whether gnuplot is present in $PATH, because we know it is.

diff --git a/eazy-gnuplot.asd b/eazy-gnuplot.asd
index 7b1c09b..4657cd6 100644
--- a/eazy-gnuplot.asd
+++ b/eazy-gnuplot.asd
@@ -37,7 +37,4 @@
                                :fill-pointer t)))
           (setf (fill-pointer seq) (read-sequence seq stream))
           seq)))
-  :perform (load-op :before (op c)
-                    (unless (zerop (nth-value 2 (uiop:run-program "which gnuplot" :ignore-error-status t)))
-                      (warn "Could not find GNUPLOT in $PATH")))
   :in-order-to ((test-op (test-op eazy-gnuplot.test))))
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<div class='path'>path: <a href='/guix/log/?id=612ed88b10d21d27473861340144cc2e98d3b2ca'>root</a>/<a href='/guix/log/nix?id=612ed88b10d21d27473861340144cc2e98d3b2ca'>nix</a>/<a href='/guix/log/nix/libstore?id=612ed88b10d21d27473861340144cc2e98d3b2ca'>libstore</a>/<a href='/guix/log/nix/libstore/globals.hh?id=612ed88b10d21d27473861340144cc2e98d3b2ca'>globals.hh</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/nix/libstore/globals.hh?id=612ed88b10d21d27473861340144cc2e98d3b2ca&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-09-08 11:49:24 +0200'>2019-09-08</span></td><td><a href='/guix/commit/nix/libstore/globals.hh?id=82f903e70f580c34503052245625354d2f097d7e'>daemon: Remove 'NIX_LIBEXEC_DIR'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-09-08 11:49:24 +0200'>2019-09-08</span></td><td><a href='/guix/commit/nix/libstore/globals.hh?id=f6919ebdc6b0ce0286814cc6ab0564b1a4c67f5f'>daemon: Run 'guix substitute' directly and assume a single substituter.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-09-08 11:49:24 +0200'>2019-09-08</span></td><td><a href='/guix/commit/nix/libstore/globals.hh?id=2e3e5d21988fc2cafb2a9eaf4b00976ea425629d'>daemon: Invoke 'guix gc --list-busy' instead of 'list-runtime-roots'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-02-04 00:03:30 +0100'>2019-02-04</span></td><td><a href='/guix/commit/nix/libstore/globals.hh?id=65d13e3043d90382f79b1780e06dc671ae451edf'>daemon: Remove unused 'NIX_DATA_DIR' environment variable.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-10-15 22:40:35 +0200'>2018-10-15</span></td><td><a href='/guix/commit/nix/libstore/globals.hh?id=6ef61cc4c30e94acbd7437f19c893f63a7112267'>daemon: Support multiplexed build output.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-10-02 23:08:30 +0200'>2018-10-02</span></td><td><a href='/guix/commit/nix/libstore/globals.hh?id=c577ac194afb4c9df76f9955aeb6118aafac6c34'>daemon: Remove unused 'Settings' fields.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-03-30 23:42:07 +0200'>2018-03-30</span></td><td><a href='/guix/commit/nix/libstore/globals.hh?id=c7589cce8d3f9fcb7769e424f341dba8fb3545d0'>daemon: Remove dead code.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-01-07 23:47:22 +0100'>2018-01-07</span></td><td><a href='/guix/commit/nix/libstore/globals.hh?id=f997137d0e2eba27bb1e2b282ee19ea474c41e12'>daemon: Make libbz2 an optional dependency.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-01-07 23:47:22 +0100'>2018-01-07</span></td><td><a href='/guix/commit/nix/libstore/globals.hh?id=29a686688674dc875775305312513405fa396a06'>daemon: Add gzip log compression.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>