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>

libIDL.spec

@@ -58,9 +58,6 @@ if [ $1 = 0 ]; then
    /sbin/install-info --quiet --delete %{_infodir}/libIDL2.info.gz %{_infodir}/dir || :
 fi
 
-%clean
-rm -rf %{buildroot}
-
 %files
 %defattr(-,root,root)
 %{_libdir}/libIDL-*.so.*