Sema: Remove unused method from FailureDiagnostic.

Author: tshortli

lib/Sema/CSDiagnostics.h

@@ -90,12 +90,6 @@ class FailureDiagnostic {
 
   ConstraintLocator *getLocator() const { return Locator; }
 
-  SourceLoc getBestAddImportFixItLocation(const Decl *Member,
-                                          SourceFile *sourceFile) const {
-    auto &engine = Member->getASTContext().Diags;
-    return engine.getBestAddImportFixItLoc(Member, sourceFile);
-  }
-
   Type getType(ASTNode node, bool wantRValue = true) const;
 
   /// Get type associated with a given ASTNode without resolving it,