rtl_arena_create's quantum_cache_max parameter (when non-zero) would have
allowed an rtl_arena to internally use an rtl_cache for chunk allocation.  (And
none of the LO-internal uses of rtl_arena_create makes use of that.)

However, with the combination of old ce906b80
"skip tricky allocators on G_SLICE=always-malloc" and recent
bc6a5d8e "Disable custom allocator", rtl_cache
unconditionally just uses malloc/free now, so the rtl_arena_create
quantum_cache_max feature has effectively become irrelevant.  As those changes
appear to have no negative consequences overall (and help remove quite a chunk
of no-longer used code), leave it at that and officially abandon the
quantum_cache_max feature.

Change-Id: I7d186a4a1589db6a73059c2be164aa81d81aef47
Reviewed-on: https://gerrit.libreoffice.org/54388Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>