Move expat LICENSE file up to third_party/expat

Everything in third_party/expat is actually first party, consisting of
build files, roll script, and customized configuration includes. Move
the LICENSE file to reflect that.

Change-Id: I44c47e5e9c9f41086d8931bae59ad6c94438cf2b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/609596
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Ravi Mistry <rmistry@google.com>
diff --git a/third_party/expat/include/expat_config/LICENSE b/third_party/expat/LICENSE
similarity index 100%
rename from third_party/expat/include/expat_config/LICENSE
rename to third_party/expat/LICENSE