GGC: Remove unused 'bool is_string' arguments to 'ggc_pch_{count,alloc,write}_object'
They're unused since the removal of 'gcc/ggc-zone.c' in 2013 Subversion r195426
(Git commit
cd030c079e5e42fe3f49261fe01f384e6b7f0111) "Remove zone allocator".
Should any future 'gcc/ggc-[...].cc' ever need this again, it'll be a conscious
decision at that time.
gcc/
* ggc-internal.h (ggc_pch_count_object, ggc_pch_alloc_object)
(ggc_pch_write_object): Remove 'bool is_string' argument.
* ggc-common.cc: Adjust.
* ggc-page.cc: Likewise.