[RISC-V][PR target/119865] Don't free ggc allocated memory

Kaiweng's patch to stop freeing riscv_arch_string was correct, but incomplete
as there's another path that was freeing that node, which is just plain wrong
for a node allocated by the GC system.

This patch removes that call to free() which fixes the test.  I've spun it in
my tester and will obviously wait for the pre-commit system to render a verdict
before moving forward.

	PR target/119865
gcc/
	* config/riscv/riscv.cc (parse_features_for_version): Do not
	explicitly free the architecture string.

gcc/config/riscv/riscv.cc

@@ -13136,9 +13136,6 @@ parse_features_for_version (tree decl,
 					  DECL_SOURCE_LOCATION (decl));
   gcc_assert (parse_res);
 
-  if (arch_string != default_opts->x_riscv_arch_string)
-    free (CONST_CAST (void *, (const void *) arch_string));
-
   cl_target_option_restore (&global_options, &global_options_set,
 			    &cur_target);
 }