Change end_psymtab_common to a method

Change end_psymtab_common to a method

This changes end_psymtab_common to be a method on partial_symtab.
This seems a little cleaner to me.

gdb/ChangeLog
2020-11-01  Tom Tromey  <tom@tromey.com>

	* dbxread.c (dbx_end_psymtab): Update.
	* dwarf2/read.c (process_psymtab_comp_unit_reader)
	(build_type_psymtabs_reader): Update.
	* xcoffread.c (xcoff_end_psymtab): Update.
	* ctfread.c (scan_partial_symbols): Update.
	* psymtab.c (sort_pst_symbols): Remove.
	(partial_symtab::end): Rename from end_psymtab_common.  Inline
	sort_pst_symbols.
	* psympriv.h (struct partial_symtab) <end>: New method.
	(end_psymtab_common): Don't declare.