Enable multi-arch Flutter Gallery on iOS (#17350)

Build universal armv7+arm64 binary for iOS now that our tooling supports
it.

examples/flutter_gallery/ios/Flutter/AppFrameworkInfo.plist

@@ -20,10 +20,6 @@
   <string>????</string>
   <key>CFBundleVersion</key>
   <string>1.0</string>
-  <key>UIRequiredDeviceCapabilities</key>
-  <array>
-    <string>arm64</string>
-  </array>
   <key>MinimumOSVersion</key>
   <string>8.0</string>
 </dict>

examples/flutter_gallery/ios/Runner.xcodeproj/project.pbxproj

@@ -442,7 +442,6 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = 9740EEB21CF90195004384FC /* Debug.xcconfig */;
 			buildSettings = {
-				ARCHS = arm64;
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ENABLE_BITCODE = NO;
 				FRAMEWORK_SEARCH_PATHS = (
@@ -464,7 +463,6 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = 7AFA3C8E1D35360C0083082E /* Release.xcconfig */;
 			buildSettings = {
-				ARCHS = arm64;
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ENABLE_BITCODE = NO;
 				FRAMEWORK_SEARCH_PATHS = (

examples/flutter_gallery/ios/Runner/Info.plist

@@ -26,10 +26,6 @@
 	<string>LaunchScreen</string>
 	<key>UIMainStoryboardFile</key>
 	<string>Main</string>
-	<key>UIRequiredDeviceCapabilities</key>
-	<array>
-		<string>arm64</string>
-	</array>
 	<key>UISupportedInterfaceOrientations</key>
 	<array>
 		<string>UIInterfaceOrientationPortrait</string>