Remove headers from gni source lists

Change-Id: Ic5542d3304ef0673e899d8a21c7bf470f7e2dad6
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/211599
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
diff --git a/skcms.gni b/skcms.gni
index a3def6e..c0ebdbe 100644
--- a/skcms.gni
+++ b/skcms.gni
@@ -5,7 +5,4 @@
 
 skcms_sources = [
   "skcms.cc",
-  "skcms.h",
-  "skcms_internal.h",
-  "src/Transform_inl.h",
 ]