Bug 1964465 - remove unused x86-debug build variant. r=bhearsum,nalexander

As far as I can tell we haven't had an android x86 debug build since at
least the taskcluster migration.

Differential Revision: https://phabricator.services.mozilla.com/D247932

testing/mozharness/configs/builds/releng_sub_android_configs/64_x86_debug.py

@@ -1,10 +0,0 @@
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-config = {
-    "stage_platform": "android-x86-debug",
-    "mozconfig_platform": "android-x86",
-    "mozconfig_variant": "debug",
-    "debug_build": True,
-}

testing/mozharness/mozharness/mozilla/building/buildbase.py

@@ -271,7 +271,6 @@ class BuildOptionParser:
         "rusttests-debug": path_base + "%s_rusttests_debug.py",
         "x86": path_base + "%s_x86.py",
         "x86-lite": path_base + "%s_x86_lite.py",
-        "x86-debug": path_base + "%s_x86_debug.py",
         "x86-profile-generate": path_base + "%s_x86_profile_generate.py",
         "x86_64": path_base + "%s_x86_64.py",
         "x86_64-lite": path_base + "%s_x86_64_lite.py",