Don't need root-config for (dist)clean; fixes

make[1]: Entering directory `test'
Makefile:20: etc/Makefile.arch: No such file or directory
make[1]: root-config: Command not found
make[1]: root-config: Command not found
make[1]: root-config: Command not found
make[1]: root-config: Command not found
make[1]: root-config: Command not found
make[1]: root-config: Command not found
make[1]: *** No rule to make target `etc/Makefile.arch'.  Stop.
when running make distclean without ROOTSYS


git-svn-id: http://root.cern.ch/svn/root/trunk@48714 27541ba8-7e3a-0410-8455-c3a389f83636