Remove lookup_objfile_from_block

Remove lookup_objfile_from_block

lookup_objfile_from_block mostly duplicates the functionality of
block_objfile, but in a less efficient way.  This patch removes this
function and changes the callers to use block_objfile instead.

Tested by the buildbot.

gdb/ChangeLog
2020-05-15  Tom Tromey  <tom@tromey.com>

	* symtab.c (lookup_language_this, lookup_symbol_aux): Use
	block_objfile.
	(lookup_objfile_from_block): Remove.
	(lookup_symbol_in_block, lookup_symbol_in_static_block)
	(lookup_global_symbol): Use block_objfile.
	* symtab.h (lookup_objfile_from_block): Don't declare.
	* printcmd.c (clear_dangling_display_expressions): Use
	block_objfile.
	* parse.c (operator_check_standard): Use block_objfile.