[analyzer] Remove BaseDeprecatedMemberUseVerifier.reportError2.

During the element model migration, the method
`BaseDeprecatedMemberUseVerifier.reportError` had to be split into a
`reportError` and a `reportError2` version, to allow for a gradual
migration to the new element model. Now that the element model
migration is complete, there is no need to keep both methods.

See:

- https://dart-review.googlesource.com/c/sdk/+/396571, which added the
  `reportError2` method.

- https://dart-review.googlesource.com/c/sdk/+/393603, which migrated
  the linter's use of `BaseDeprecatedMemberUseVerifier`.

- https://dart-review.googlesource.com/c/sdk/+/402201, which migrated
  the analyzer's use of `BaseDeprecatedMemberUseVerifier`.

Change-Id: I6a6a69641640a2865922fc9b3142e8160e6d4ea6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/450142
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/lib/src/error/deprecated_member_use_verifier.dart

@@ -111,18 +111,7 @@ abstract class BaseDeprecatedMemberUseVerifier {
     Element element,
     String displayName,
     String? message,
-  ) {
-    reportError2(errorEntity, element, displayName, message);
-  }
-
-  void reportError2(
-    SyntacticEntity errorEntity,
-    Element element,
-    String displayName,
-    String? message,
-  ) {
-    reportError(errorEntity, element, displayName, message);
-  }
+  );
 
   void simpleIdentifier(SimpleIdentifier node) {
     // Don't report declared identifiers.

pkg/linter/lib/src/rules/deprecated_member_use_from_same_package.dart

@@ -55,7 +55,7 @@ class _DeprecatedMemberUseVerifier extends BaseDeprecatedMemberUseVerifier {
   _DeprecatedMemberUseVerifier(this._rule, this._workspacePackage);
 
   @override
-  void reportError2(
+  void reportError(
     SyntacticEntity errorEntity,
     Element element,
     String displayName,