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>

libesmtp.spec

@@ -75,9 +75,6 @@ rm $RPM_BUILD_ROOT/%{_libdir}/esmtp-plugins/*.la
 install -p -m644 -D libesmtp.pc $RPM_BUILD_ROOT%{_libdir}/pkgconfig/libesmtp.pc
 
 
-%clean
-rm -rf $RPM_BUILD_ROOT
-
 %post -p /sbin/ldconfig
 
 %postun -p /sbin/ldconfig