Remove quick_symbol_functions::expand_symtabs_for_function

Remove quick_symbol_functions::expand_symtabs_for_function

This removes quick_symbol_functions::expand_symtabs_for_function,
replacing it with a call to expand_symtabs_matching.  As with the
previous patches, the implementation is consolidated in the objfile
method.

gdb/ChangeLog
2021-04-17  Tom Tromey  <tom@tromey.com>

	* symfile-debug.c (objfile::expand_symtabs_for_function):
	Rewrite.
	* quick-symbol.h (struct quick_symbol_functions)
	<expand_symtabs_for_function>: Remove.
	* psymtab.c (psymbol_functions::expand_symtabs_for_function):
	Remove.
	* psympriv.h (struct psymbol_functions)
	<expand_symtabs_for_function>: Remove.
	* objfiles.h (struct objfile) <expand_symtabs_for_function>:
	Update comment.
	* dwarf2/read.c (struct dwarf2_gdb_index)
	<expand_symtabs_for_function>: Remove.
	(struct dwarf2_debug_names_index) <expand_symtabs_for_function>:
	Remove.
	(find_slot_in_mapped_hash): Remove.
	(dw2_symtab_iter_init_common): Merge with dw2_symtab_iter_init.
	(dw2_symtab_iter_init): Remove one overload.
	(dwarf2_gdb_index::expand_symtabs_for_function)
	(dwarf2_debug_names_index::expand_symtabs_for_function): Remove.