Revert "Enable -Wunused-but-set-variable."

This reverts commit 54738b8.

Reason for revert: Likely cause for tree closure from this build: https://ci.chromium.org/ui/p/chromium/builders/ci/Mac%20Builder/146453/overview

Original change's description:
> Enable -Wunused-but-set-variable.
>
> Bug: 1203071
> Change-Id: I5e82348074c2a06392595cf22aadfb1157040689
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3228315
> Commit-Queue: Peter Kasting <pkasting@chromium.org>
> Reviewed-by: Dirk Pranke <dpranke@google.com>
> Cr-Commit-Position: refs/heads/main@{#932587}

Bug: 1203071
Change-Id: I0cd344a69bfeb33b60a7dbbcb4a89f763b93d8a3
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3229674
Auto-Submit: Emily Shack <emshack@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Guillaume Jenkins <gujen@google.com>
Reviewed-by: Emily Shack <emshack@chromium.org>
Reviewed-by: Guillaume Jenkins <gujen@google.com>
Owners-Override: Guillaume Jenkins <gujen@google.com>
Cr-Commit-Position: refs/heads/main@{#932592}

build/config/compiler/BUILD.gn

@@ -1530,6 +1530,10 @@ config("default_warnings") {
         # NaCl does not support flags from ToT.
         if (!is_nacl) {
           cflags += [
+            # TODO(https://crbug.com/1203071): Clean up and enable.
+            "-Wno-unused-but-set-parameter",
+            "-Wno-unused-but-set-variable",
+
             # TODO(https://crbug.com/1255745): Clean up, enable.
             "-Wno-bitwise-instead-of-logical",
           ]
@@ -1681,9 +1685,6 @@ config("no_chromium_code") {
     ]
     if (!is_nacl && (current_toolchain == host_toolchain || !use_xcode_clang)) {
       cflags += [
-        # Disabled for similar reasons as -Wunused-variable.
-        "-Wno-unused-but-set-variable",
-
         # TODO(https://crbug.com/1202159): Clean up and enable.
         "-Wno-misleading-indentation",
       ]