AST: Don't need to call getCanonicalType() in TypeBase::isPlaceholder()
AST: Don't need to call getCanonicalType() in TypeBase::isPlaceholder()

apple/swift,apple/swift,roambotics/swift,apple/swift,roambotics/swift,roambotics/swift,roambotics/swift,roambotics/swift,apple/swift,roambotics/swift,apple/swift,apple/swift