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>

libasyncns.spec

@@ -36,9 +36,6 @@ make DESTDIR=$RPM_BUILD_ROOT install
 find $RPM_BUILD_ROOT \( -name *.a -o -name *.la \) -exec rm {} \;
 rm -rf $RPM_BUILD_ROOT/usr/share/doc/libasyncns/
 
-%clean
-rm -rf $RPM_BUILD_ROOT
-
 %files
 %defattr(-,root,root)
 %doc README LICENSE