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>

perl-Declare-Constraints-Simple.spec

@@ -78,9 +78,6 @@ find %{buildroot} -type f -name .packlist -exec rm -f {} \;
 %check
 make test
 
-%clean
-rm -rf %{buildroot}
-
 %files
 %doc Changes README t/
 %{perl_vendorlib}/Declare/