* regcache.c (struct regcache_descr): Remove outdated comment.
(init_regcache_descr): Remove sizeof_raw_register_valid_p
overallocate hack.
(regcache_xmalloc): Rename to ...
(regcache_xmalloc_1): ... this. Add `readonly_p' parameter.
Allocate the regcache type accordingly.
(regcache_xmalloc): New as wrapper around regcache_xmalloc_1.
(regcache_xfree): Asser the source is also readonly. Copy sizeof
cooked registers, not raw.
(regcache_dup_no_passthrough): Delete.
(get_thread_arch_regcache): Use regcache_xmalloc_1.
* h8300-tdep.c (h8300_push_dummy_call): Tweak comment to not
mention obsolete write_register_bytes.
* regcache.h (regcache_dup_no_passthrough): Delete declaration.