don't include unused header

Change-Id: Ie58952c84341bdf7116d00c4e415dad9c6dda778
Reviewed-on: https://skia-review.googlesource.com/c/libgifcodec/+/259280
Reviewed-by: Hal Canary <halcanary@google.com>
diff --git a/SkLibGifCodec.cpp b/SkLibGifCodec.cpp
index d4f8790..e6fab5c 100644
--- a/SkLibGifCodec.cpp
+++ b/SkLibGifCodec.cpp
@@ -36,7 +36,6 @@
 #include "src/codec/SkCodecPriv.h"
 #include "src/codec/SkColorTable.h"
 #include "src/codec/SkSwizzler.h"
-#include "src/core/SkMakeUnique.h"
 
 #include <algorithm>