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 59cc4834e53565da1de4a7b615ed8890ed55c7da
  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.

gdb/go-lang.c

@@ -638,6 +638,10 @@ public:
 	    && go_classify_struct_type (type) == GO_TYPE_STRING);
   }
 
+  /* See language.h.  */
+
+  bool store_sym_names_in_linkage_form_p () const override
+  { return true; }
 };
 
 /* Single instance of the Go language class.  */