docs/releasing: remove "git clean" step

release.sh from master, does not require the tree to be clean.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>

docs/releasing.html

@@ -438,8 +438,7 @@ Commit these changes and push the branch.
 <h3>Use the release.sh script from xorg util-macros</h3>
 
 <p>
-Ensure that the mesa git tree is clean via <code>git clean -fXd</code> and
-start the release process.
+Start the release process.
 </p>
 <pre>
 	../relative/path/to/release.sh . # append --dist if you've already done distcheck above