Remove quick_symbol_functions::lookup_symbol

Remove quick_symbol_functions::lookup_symbol

This removes quick_symbol_functions, replacing it with calls to
expand_symtabs_matching.  Because the replacement is somewhat verbose,
objfile::lookup_symbol is not removed.  This consolidates some
duplicated code into this one spot.

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

	* symfile-debug.c (objfile::lookup_symbol): Rewrite.
	* quick-symbol.h (struct quick_symbol_functions) <lookup_symbol>:
	Remove.
	* psymtab.c (psymbol_functions::lookup_symbol): Remove.
	* psympriv.h (struct psymbol_functions) <lookup_symbol>: Remove.
	* objfiles.h (struct objfile) <lookup_symbol>: Add comment.
	* dwarf2/read.c (struct dwarf2_gdb_index) <lookup_symbol>:
	Remove.
	(struct dwarf2_debug_names_index) <lookup_symbol>: Remove.
	(dwarf2_gdb_index::lookup_symbol)
	(dwarf2_debug_names_index::lookup_symbol): Remove.