clean up stray #undef

There was a time when we used to #define VECTOR(...) to make
it easy to add opcodes, but not since

    https://skia-review.googlesource.com/c/skia/+/299682

Oddly we never #undef'd VECTOR_MATRIX.

Change-Id: I4a68d29a0ee6c34ee421e1bc4e76155d110de6fd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/310324
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/src/sksl/SkSLByteCode.h b/src/sksl/SkSLByteCode.h
index 845a6a8..2540f7a 100644
--- a/src/sksl/SkSLByteCode.h
+++ b/src/sksl/SkSLByteCode.h
@@ -155,7 +155,6 @@
     kLoopBreak,
     kLoopContinue,
 };
-#undef VECTOR
 
 class ByteCodeFunction {
 public: