Revert Twitter Auth deprecation because devepler may want to build their own sign in flow (#2765)

Author: Yue-Wang-Google

Firebase/Auth/Source/Auth Provider/Twitter/FIRTwitterAuthCredential.h

@@ -23,7 +23,6 @@ NS_ASSUME_NONNULL_BEGIN
 /** @class FIRTwitterAuthCredential
     @brief Internal implementation of FIRAuthCredential for Twitter credentials.
  */
-DEPRECATED_MSG_ATTRIBUTE("Please use FIROAuthCredential instead of FIRTwitterAuthCredential.")
 @interface FIRTwitterAuthCredential : FIRAuthCredential <NSSecureCoding>
 
 /** @property token

Firebase/Auth/Source/Auth Provider/Twitter/FIRTwitterAuthCredential.m

@@ -22,9 +22,6 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wdeprecated-implementations"
-
 @interface FIRTwitterAuthCredential ()
 
 - (nullable instancetype)initWithProvider:(NSString *)provider NS_UNAVAILABLE;
@@ -73,6 +70,4 @@ - (void)encodeWithCoder:(NSCoder *)aCoder {
 
 @end
 
-#pragma clang diagnostic pop
-
 NS_ASSUME_NONNULL_END

Firebase/Auth/Source/Auth Provider/Twitter/FIRTwitterAuthProvider.m

@@ -23,9 +23,6 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wdeprecated-implementations"
-
 @implementation FIRTwitterAuthProvider
 
 - (instancetype)init {
@@ -40,6 +37,4 @@ + (FIRAuthCredential *)credentialWithToken:(NSString *)token secret:(NSString *)
 
 @end
 
-#pragma clang diagnostic pop
-
 NS_ASSUME_NONNULL_END

Firebase/Auth/Source/Public/FIRTwitterAuthProvider.h

@@ -23,20 +23,15 @@ NS_ASSUME_NONNULL_BEGIN
 /**
     @brief A string constant identifying the Twitter identity provider.
  */
-extern NSString *const FIRTwitterAuthProviderID NS_SWIFT_NAME(TwitterAuthProviderID)
-    DEPRECATED_MSG_ATTRIBUTE("Please use \"twitter.com\" instead.");
-
+extern NSString *const FIRTwitterAuthProviderID NS_SWIFT_NAME(TwitterAuthProviderID);
 /**
     @brief A string constant identifying the Twitter sign-in method.
  */
-extern NSString *const _Nonnull FIRTwitterAuthSignInMethod NS_SWIFT_NAME(TwitterAuthSignInMethod)
-    DEPRECATED_MSG_ATTRIBUTE("Please use \"twitter.com\" instead.");
-
+extern NSString *const _Nonnull FIRTwitterAuthSignInMethod NS_SWIFT_NAME(TwitterAuthSignInMethod);
 
 /** @class FIRTwitterAuthProvider
     @brief Utility class for constructing Twitter credentials.
  */
-DEPRECATED_MSG_ATTRIBUTE("Please use FIROAuthProvider instead of FIRTwitterAuthProvider.")
 NS_SWIFT_NAME(TwitterAuthProvider)
 @interface FIRTwitterAuthProvider : NSObject