Remove unnecessary clean-up of buildroot

rhel5 required to clean buildroot in install section.
The %clean section is not required for F-13 and above, and EPEL 6 and
above. EPEL 5 MUST have a %clean section that cleans the buildroot:

https://fedoraproject.org/wiki/EPEL:Packaging#Prepping_BuildRoot_For_.25install

sssd.spec

@@ -598,7 +598,6 @@ make %{?_smp_mflags} check VERBOSE=yes
 unset CK_TIMEOUT_MULTIPLIER
 
 %install
-rm -rf $RPM_BUILD_ROOT
 
 sed -i -e 's:/usr/bin/python:/usr/bin/python3:' src/tools/sss_obfuscate
 
@@ -706,10 +705,6 @@ do
     cat sssd_$provider.lang
 done
 
-
-%clean
-rm -rf $RPM_BUILD_ROOT
-
 %files
 %defattr(-,root,root,-)
 %doc COPYING