Remove MAIN_NIB_FILE from Info.plist because the substitution is broken

BUG=webrtc:7943

Review-Url: https://codereview.webrtc.org/2965193002
Cr-Commit-Position: refs/heads/master@{#18915}

webrtc/test/ios/Info.plist

diff --git a/webrtc/test/ios/Info.plist b/webrtc/test/ios/Info.plist
index 4f6ae58..e02ce91 100644
--- a/webrtc/test/ios/Info.plist
+++ b/webrtc/test/ios/Info.plist
@@ -27,8 +27,6 @@
 		<key>NSAllowsArbitraryLoads</key>
 		<true/>
 	</dict>
-	<key>NSMainNibFile</key>
-	<string>${MAIN_NIB_FILE}</string>
 	<key>UIFileSharingEnabled</key>
 	<true/>
 	<key>UISupportedInterfaceOrientation</key>