Remove the "listhead" argument from finish_block

Remove the "listhead" argument from finish_block

finish_block is only ever called with "&local_symbols" as the
"listhead" argument.  So, remove this argument.

gdb/ChangeLog
2018-07-20  Tom Tromey  <tom@tromey.com>

	* xcoffread.c (read_xcoff_symtab): Update.
	* dwarf2read.c (read_func_scope, read_lexical_block_scope):
	Update.
	* dbxread.c (process_one_symbol): Update.
	* coffread.c (coff_symtab_read): Update.
	* buildsym.h (finish_block): Update.
	* buildsym.c (finish_block): Remove "listhead" argument.
	(end_symtab_get_static_block): Update.