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>

R-GenomicRanges.spec

@@ -40,9 +40,6 @@ rm -f %{buildroot}%{rlibdir}/R.css
 # suggests to have R-BSgenome
 #%%{_bindir}/R CMD check %%{packname}
 
-%clean
-rm -rf %{buildroot}
-
 %files
 %defattr(-, root, root, -)
 %dir %{rlibdir}/%{packname}/