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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<tr><td><span title='2021-05-06 09:37:34 +0200'>2021-05-06</span></td><td><a href='/guix/commit/gnu/packages/authentication.scm?id=37fd82177ef33f2d3331f14055c6302001cd7c04'>gnu: oath-toolkit: Build libpskc and pskctool.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/authentication.scm (oath-toolkit)[arguments]:
Add "--enable-pskc" and "--with-xmlsec-crypto-engine=openssl"
to #:configure-flags.
[native-inputs]: Add libltdl.
[inputs]: Add openssl and xmlsec-openssl.
[description]: Document the two new features.

Signed-off-by: Tobias Geerinckx-Rice &lt;me@tobias.gr&gt;
</span></span></td><td>Simon Josefsson via Guix-patches via</td></tr>
<tr><td><span title='2021-05-03 22:23:59 +0200'>2021-05-03</span></td><td><a href='/guix/commit/gnu/packages/authentication.scm?id=6e43922f35cac9c230e042b6cd4318501b66ba4b'>gnu: oath-toolkit: Update to 2.6.7.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/authentication.scm (oath-toolkit): Update to 2.6.7.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2021-03-04 17:07:47 +0100'>2021-03-04</span></td><td><a href='/guix/commit/gnu/packages/authentication.scm?id=cb93d420cd000a9e5ce1a6201bffff6c5babc168'>gnu: oath-toolkit: Update to 2.6.6.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/authentication.scm (oath-toolkit): Update to 2.6.6.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>