Merge pull request swiftlang#31550 from AnthonyLatsis/dead-alias

NFC: Remove leftover alias

Author: AnthonyLatsis

lib/Sema/TypeChecker.h

@@ -52,11 +52,6 @@ namespace constraints {
   class SolutionResult;
 }
 
-/// A mapping from substitutable types to the protocol-conformance
-/// mappings for those types.
-using ConformanceMap =
-    llvm::DenseMap<SubstitutableType *, SmallVector<ProtocolConformance *, 2>>;
-
 /// Special-case type checking semantics for certain declarations.
 enum class DeclTypeCheckingSemantics {
   /// A normal declaration.