language_get_symbol_name_matcher -> get_symbol_name_matcher

Rename language_get_symbol_name_matcher -> get_symbol_name_matcher,
since the function is no longer a straight "language method".

gdb/ChangeLog:
2018-01-10  Pedro Alves  <palves@redhat.com>

	* language.h (language_get_symbol_name_matcher): Rename ...
	(get_symbol_name_matcher): ... this.
	* language.c (language_get_symbol_name_matcher): Ditto.
	* dictionary.c, linespec.c, minsyms.c, psymtab.c, symtab.c: All
	callers adjusted.