cpupower tool: remove use of undefined variables from the clean target of the top makefile

UTIL_BINS and IDLE_OBJS variables are not defined at all, so
there's no need to remove their content from the 'clean' target.

Signed-off-by: Franck Bui-Huu <[e-mail]>
Signed-off-by: Dominik Brodowski <[e-mail]>

tools/power/cpupower/Makefile

···
 clean:
 	-find . \( -not -type d \) -and \( -name '*~' -o -name '*.[oas]' \) -type f -print \
 	 | xargs rm -f
-	-rm -f $(UTIL_BINS)
-	-rm -f $(IDLE_OBJS)
 	-rm -f cpupower
 	-rm -f libcpupower.so*
 	-rm -rf po/*.gmo po/*.pot