Remove MPL from Android's license_kinds

Change-Id: I8942814623e4d66df3a8810c68fa36aaab5bd578
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/504538
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Heather Miller <hcm@google.com>

gn/gn_to_bp.py

@@ -64,7 +64,6 @@ license {
         "SPDX-license-identifier-CC0-1.0",
         "SPDX-license-identifier-FTL",
         "SPDX-license-identifier-MIT",
-        "SPDX-license-identifier-MPL",
         "legacy_unencumbered",
     ],
     license_text: [