Bug 1556738 - Tighten up some clang-cl warning allowances r=nalexander

Remove a few no-longer-necessary `AllowCompilerWarnings()` before anything that depends upon them sneaks in.

Differential Revision: https://phabricator.services.mozilla.com/D33631

--HG--
extra : moz-landing-system : lando

browser/app/winlauncher/test/moz.build

@@ -27,6 +27,3 @@ if CONFIG['CC_TYPE'] in ('gcc', 'clang'):
     LDFLAGS += [
         '-municode',
     ]
-
-if CONFIG['CC_TYPE'] == 'clang-cl':
-    AllowCompilerWarnings()  # workaround for bug 1090497

dom/media/gtest/moz.build

@@ -110,8 +110,5 @@ FINAL_LIBRARY = 'xul-gtest'
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wno-error=shadow']
 
-if CONFIG['CC_TYPE'] == 'clang':
+if CONFIG['CC_TYPE'] in ('clang', 'clang-cl'):
     CXXFLAGS += ['-Wno-unused-private-field']
-
-if CONFIG['CC_TYPE'] == 'clang-cl':
-    AllowCompilerWarnings()  # workaround for bug 1090497

toolkit/mozapps/update/common/moz.build

@@ -63,9 +63,6 @@ SOURCES += [
     'updatecommon.cpp',
 ]
 
-if CONFIG['CC_TYPE'] == 'clang-cl':
-    AllowCompilerWarnings()  # workaround for bug 1090497
-
 LOCAL_INCLUDES += [
     '/other-licenses/nsis/Contrib/CityHash/cityhash',
 ]