Remove buildsym_init

Remove buildsym_init

Now that buildsym_init does nothing, it can be removed.

gdb/ChangeLog
2018-07-20  Tom Tromey  <tom@tromey.com>

	* coffread.c (coff_symtab_read): Update.
	* xcoffread.c (xcoff_psymtab_to_symtab_1): Update.
	(xcoff_new_init): Update.
	* mipsread.c (mipscoff_new_init): Update.
	* mdebugread.c (mdebug_build_psymtabs): Update.
	* elfread.c (elf_new_init): Update.
	* dwarf2read.c (process_full_comp_unit, process_full_type_unit):
	Update.
	* dbxread.c (dbx_new_init, dbx_psymtab_to_symtab_1)
	(coffstab_build_psymtabs, elfstab_build_psymtabs)
	(stabsect_build_psymtabs): Update.
	* buildsym.h (buildsym_init): Don't declare.
	* buildsym.c: Update comment.
	(prepare_for_building): Remove.
	(start_symtab, restart_symtab): Update.
	(reset_symtab_globals): Update comment.
	(buildsym_init): Remove.