Remove %clean section

None of currently supported distributions need that.
Last one was EL5 which is EOL for a while.

Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

lv2.spec

@@ -89,9 +89,6 @@ for f in COPYING NEWS README.md ; do
     install -p -m0644 $f %{buildroot}%{_pkgdocdir}
 done
 
-%clean
-rm -rf %buildroot
-
 %files
 # don't include doc files via %%doc here (bz 913540)
 %dir %{_pkgdocdir}