[cxx-interop] Remove dead code: isCxxInteropCompatVersionAtLeast

rdar://165919353

Author: egorzhdan

include/swift/Basic/LangOptions.h

@@ -753,13 +753,6 @@ namespace swift {
       return EffectiveLanguageVersion.isVersionAtLeast(major, minor);
     }
 
-    /// Whether the C++ interoperability compatibility version is at least
-    /// 'major'.
-    bool isCxxInteropCompatVersionAtLeast(unsigned major,
-                                          unsigned minor = 0) const {
-      return cxxInteropCompatVersion.isVersionAtLeast(major, minor);
-    }
-
     /// Sets the "_hasAtomicBitWidth" conditional.
     void setHasAtomicBitWidth(llvm::Triple triple);
 

lib/ClangImporter/ImporterImpl.h

@@ -624,17 +624,6 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
   void getMangledName(clang::MangleContext *mangler,
                       const clang::NamedDecl *clangDecl, raw_ostream &os);
 
-  /// Whether the C++ interoperability compatibility version is at least
-  /// 'major'.
-  ///
-  /// Use the
-  /// `isCxxInteropCompatVersionAtLeast(version::getUpcomingCxxInteropCompatVersion())`
-  /// check when making a source breaking C++ interop change.
-  bool isCxxInteropCompatVersionAtLeast(unsigned major,
-                                        unsigned minor = 0) const {
-    return SwiftContext.LangOpts.isCxxInteropCompatVersionAtLeast(major, minor);
-  }
-
 private:
   /// The Importer may be configured to load modules of a different OS Version
   /// than the underlying Swift compilation. This is the `TargetOptions`