Removes unused Fir_authPhoneNumber (firebase#277)

Removes references of unused Fir_authPhoneNumber and accompanying class.

Author: protocol86

Example/Auth/Tests/FIRPhoneAuthProviderTests.m

@@ -43,7 +43,6 @@
 #import "FIRVerifyClientResponse.h"
 #import "OCMStubRecorder+FIRAuthUnitTests.h"
 #import "Phone/FIRPhoneAuthCredential_Internal.h"
-#import "Phone/NSString+FIRAuth.h"
 
 @import SafariServices;
 
@@ -328,7 +327,6 @@ - (void)testVerifyPhoneNumber {
     XCTAssertTrue([NSThread isMainThread]);
     XCTAssertNil(error);
     XCTAssertEqualObjects(verificationID, kTestVerificationID);
-    XCTAssertEqualObjects(verificationID.fir_authPhoneNumber, kTestPhoneNumber);
     [expectation fulfill];
   }];
   [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];
@@ -443,7 +441,6 @@ - (void)testVerifyPhoneNumberUIDelegate {
     XCTAssertTrue([NSThread isMainThread]);
     XCTAssertNil(error);
     XCTAssertEqualObjects(verificationID, kTestVerificationID);
-    XCTAssertEqualObjects(verificationID.fir_authPhoneNumber, kTestPhoneNumber);
     [expectation fulfill];
   }];
   [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];
@@ -711,7 +708,6 @@ - (void)testVerifyClient {
     XCTAssertTrue([NSThread isMainThread]);
     XCTAssertNil(error);
     XCTAssertEqualObjects(verificationID, kTestVerificationID);
-    XCTAssertEqualObjects(verificationID.fir_authPhoneNumber, kTestPhoneNumber);
     [expectation fulfill];
   }];
   [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];
@@ -893,7 +889,6 @@ - (void)testSendVerificationCodeSuccessFulRetry {
                     completion:^(NSString *_Nullable verificationID, NSError *_Nullable error) {
     XCTAssertNil(error);
     XCTAssertEqualObjects(verificationID, kTestVerificationID);
-    XCTAssertEqualObjects(verificationID.fir_authPhoneNumber, kTestPhoneNumber);
     [expectation fulfill];
   }];
   [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];

Firebase/Auth/Source/AuthProviders/Phone/FIRPhoneAuthProvider.m

@@ -20,7 +20,6 @@
 
 #import "FIRLogger.h"
 #import "FIRPhoneAuthCredential_Internal.h"
-#import "NSString+FIRAuth.h"
 #import "FIRApp.h"
 #import "FIRAuthAPNSToken.h"
 #import "FIRAuthAPNSTokenManager.h"
@@ -194,8 +193,6 @@ - (void)verifyPhoneNumber:(NSString *)phoneNumber
               callBackOnMainThread(nil, error);
               return;
             }
-            // Associate the phone number with the verification ID.
-            response.verificationID.fir_authPhoneNumber = phoneNumber;
             callBackOnMainThread(response.verificationID, nil);
           }];
         }];
@@ -381,8 +378,6 @@ - (void)verifyClientAndSendVerificationCodeToPhoneNumber:(NSString *)phoneNumber
         callback(nil, error);
         return;
       }
-      // Associate the phone number with the verification ID.
-      response.verificationID.fir_authPhoneNumber = phoneNumber;
       callback(response.verificationID, nil);
     }];
   }];