Remove check for working malloc_set_state

Remove check for working malloc_set_state

This check was added to 'malloc_initialize_hook' in order to "insulate
Emacs better from configuration screwups" (commit b4788b9394f3).  With
unexec gone, we no longer use 'malloc_set_state', and thus don't need
this check.

Note that this patch removes the last uses of the deprecated glibc
functions 'malloc_set_state' and 'malloc_get_state' from our code.

* src/alloc.c (malloc_initialize_hook) [DOUG_LEA_MALLOC]:
Remove check for working 'malloc_set_state'.
(alloc_unexec_pre) [DOUG_LEA_MALLOC]: Delete unused function.
(alloc_unexec_post) [DOUG_LEA_MALLOC]: Delete function.
(malloc_state_ptr) [DOUG_LEA_MALLOC]: Delete variable.
* configure.ac (emacs_cv_var_doug_lea_malloc): Don't check for
malloc_set_state and malloc_get_state.

(cherry picked from commit 892be3b3d7a459808ee47709d0f4e7f65566a6e5)