Remove MAIN_NIB_FILE from Info.plist because the substitution is broken

webrtc/test/ios/Info.plist

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
 <dict>
         <key>CFBundleDevelopmentRegion</key>
         <string>English</string>
         <key>CFBundleDisplayName</key>
         <string>${PRODUCT_NAME}</string>
         <key>CFBundleExecutable</key>
         <string>${EXECUTABLE_NAME}</string>
         <key>CFBundleIdentifier</key>
         <string>${IOS_BUNDLE_ID_PREFIX}.gtest.${GTEST_BUNDLE_ID_SUFFIX:rfc1034identifier}</string>
         <key>CFBundleInfoDictionaryVersion</key>
         <string>6.0</string>
         <key>CFBundleName</key>
         <string>${PRODUCT_NAME}</string>
         <key>CFBundlePackageType</key>
         <string>APPL</string>
         <key>CFBundleSignature</key>
         <string>????</string>
         <key>CFBundleVersion</key>
         <string>1.0</string>
         <key>LSRequiresIPhoneOS</key>
         <true/>
         <key>NSAppTransportSecurity</key>
         <dict>
                 <key>NSAllowsArbitraryLoads</key>
                 <true/>
         </dict>
-        <key>NSMainNibFile</key>
-        <string>${MAIN_NIB_FILE}</string>
         <key>UIFileSharingEnabled</key>
         <true/>
         <key>UISupportedInterfaceOrientation</key>
         <array>
                 <string>UIInterfaceOrientationPortrait</string>
                 <string>UIInterfaceOrientationLandscapeLeft</string>
                 <string>UIInterfaceOrientationLandscapeRight</string>
         </array>
         <key>UIBackgroundModes</key>
         <array>
                 <string>fetch</string>
         </array>
         <key>NSMicrophoneUsageDescription</key>
         <string>For testing purposes</string>
 </dict>
 </plist>