gdb: Override store_sym_names_in_linkage_form_p for Go language

When store_sym_names_in_linkage_form_p was introduced in this commit:

  commit 59cc4834
  Date:   Tue Mar 27 08:57:16 2018 -0500

      problem looking up some symbols when they have a linkage name

A special case was left behind for Go, however, this special case was
not really needed anymore, it could be handled by having
store_sym_names_in_linkage_form_p return the true for go, instead of
false.

This commit overrides store_sym_names_in_linkage_form_p for Go, and
then removes the special case.  As store_sym_names_in_linkage_form_p
is only called once throughout GDB this should be perfectly safe.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* dwarf2/read.c (dwarf2_physname): Remove special case for
	language_go.
	* go-lang.c (go_language::store_sym_names_in_linkage_form_p): New
	member function.