Remote Config `pod spec lint` fixes (#3717)

* Fix ExperimentPayload.pbobjc.h imports

* RemoteConfig tests: add missing headers to spec.

* Revert ExperimentPayload.pbobjc.h import for ABTesting sources.

FirebaseRemoteConfig.podspec

@@ -59,7 +59,8 @@ app update.
         'FirebaseRemoteConfig/Tests/Unit/RCNRemoteConfigTest.m',
 #        'FirebaseRemoteConfig/Tests/Unit/RCNThrottlingTests.m',
         'FirebaseRemoteConfig/Tests/Unit/RCNTestUtilities.m',
-        'FirebaseRemoteConfig/Tests/Unit/RCNUserDefaultsManagerTests.m'
+        'FirebaseRemoteConfig/Tests/Unit/RCNUserDefaultsManagerTests.m',
+        'FirebaseRemoteConfig/Tests/Unit/RCNTestUtilities.h'
     # Supply plist custom plist testing.
     unit_tests.resources =
         'FirebaseRemoteConfig/Tests/Unit/Defaults-testInfo.plist',

FirebaseRemoteConfig/Tests/Unit/RCNConfigExperimentTest.m

@@ -25,11 +25,11 @@
 #import "FirebaseRemoteConfig/Sources/RCNConfigValue_Internal.h"
 #import "FirebaseRemoteConfig/Tests/Unit/RCNTestUtilities.h"
 
+#import <FirebaseABTesting/ExperimentPayload.pbobjc.h>
 #import <FirebaseABTesting/FIRExperimentController.h>
 
 #import <FirebaseAnalyticsInterop/FIRAnalyticsInterop.h>
 #import <OCMock/OCMock.h>
-#import "FirebaseABTesting/Sources/Protos/developers/mobile/abt/proto/ExperimentPayload.pbobjc.h"
 #import "FirebaseRemoteConfig/Sources/Protos/wireless/android/config/proto/Config.pbobjc.h"
 
 // Surface the internal FIRExperimentController initializer.