nir: Use remove_and_dce for nir_shader_lower_instructions().

Reduces the work that other shader passes have to do to look at dead code,
and possibly extra rounds around the optimization loop if dce wasn't the
last pass in it.

shader-db runtime -1.12919% +/- 0.264337% (n=49) on SKL.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11628>

src/compiler/nir/nir.c

@@ -2003,7 +2003,7 @@ nir_function_impl_lower_instructions(nir_function_impl *impl,
             nir_if_rewrite_condition(use_src->parent_if, new_src);
 
          if (nir_ssa_def_is_unused(old_def)) {
-            iter = nir_instr_remove(instr);
+            iter = nir_instr_remove_and_dce(instr);
          } else {
             iter = nir_after_instr(instr);
          }
@@ -2017,7 +2017,7 @@ nir_function_impl_lower_instructions(nir_function_impl *impl,
          if (new_def == NIR_LOWER_INSTR_PROGRESS_REPLACE) {
             /* Only instructions without a return value can be removed like this */
             assert(!old_def);
-            iter = nir_instr_remove(instr);
+            iter = nir_instr_remove_and_dce(instr);
             progress = true;
          } else
             iter = nir_after_instr(instr);