[Reflection] Remove useless TaggedUnion.h include. Comment swift_metadata_allocation_tag.

Author: mikeash

include/swift/Reflection/ReflectionContext.h

@@ -24,7 +24,6 @@
 #include "llvm/Object/COFF.h"
 
 #include "swift/ABI/Enum.h"
-#include "swift/Basic/TaggedUnion.h"
 #include "swift/Remote/MemoryReader.h"
 #include "swift/Remote/MetadataReader.h"
 #include "swift/Reflection/Records.h"

include/swift/SwiftRemoteMirror/SwiftRemoteMirrorTypes.h

@@ -141,6 +141,7 @@ typedef struct swift_childinfo {
   swift_typeref_t TR;
 } swift_childinfo_t;
 
+// Values here match the values from MetadataAllocatorTags in Metadata.h.
 enum swift_metadata_allocation_tag {
   SWIFT_GENERIC_METADATA_CACHE_ALLOCATION = 14,
 };