Remove double-colon from clean target which causes breakage in reverse-depends.

--- a/lib/petsc/conf/rules
+++ b/lib/petsc/conf/rules
@@ -34,7 +34,7 @@
               *.class *.ouit *.ad.* g_* silly.cmp *.tmp.* *.ilk *.pdb *.inst.c *.rej *.gcda *.gcno
 	@-${RM} -rf ${CLEANDIRS} *.dSYM AD_cache SunWS_cache
 
-clean:: clean-legacy
+clean: clean-legacy
 
 #
 #  These rules are for compiling the test examples.
--- a/makefile
+++ b/makefile
@@ -282,7 +282,7 @@
 allclean:
 	-@${OMAKE} -f gmakefile clean
 
-clean:: allclean
+clean: allclean
 
 distclean:
 	@if [ -f ${PETSC_DIR}/${PETSC_ARCH}/lib/petsc/conf/reconfigure-${PETSC_ARCH}.py ]; then \