Avoid some copying in psymtab.c

I noticed that psymtab.c was always copying the search string in
psymtab_search_name, even when it wasn't necessary.  This patch
removes this function in favor of using the make_ignore_params feature
of lookup_name_info.

Once I had done that, I noticed that lookup_partial_symbol was
creating a lookup_name_info.  However, this function called in loops,
causing even more excess allocation.  This patch further fixes this by
hosting the creation of the lookup_name_info into the callers.

gdb/ChangeLog
2020-04-01  Tom Tromey  <tromey@adacore.com>

	* psymtab.c (psymtab_search_name): Remove function.
	(psym_lookup_symbol): Create search name and lookup name here.
	(lookup_partial_symbol): Remove "name" parameter; add
	lookup_name.
	(psym_expand_symtabs_for_function): Update.