Add end_psymtab_common, have all debug info readers call it.

gdb/ChangeLog:

	* dbxread.c (dbx_end_psymtab): Renamed from end_psymtab.  All callers
	updated.  Call end_psymtab_common.
	* dwarf2read.c (process_psymtab_comp_unit_reader): Call
	end_psymtab_common.
	(build_type_psymtabs_reader): Ditto.
	* psympriv.h (sort_pst_symbols): Delete.
	(end_psymtab_common): Declare.
	* psymtab.c (sort_pst_symbols): Make static.
	(end_psymtab_common): New function.
	* xcoffread.c (xcoff_end_psymtab): Call end_psymtab_common.