[Data Sharing] Combine BUILD files under data_sharing/android

Combine data_sharing/BUILD.gn and data_sharing/android/BUILD.gn.

Bug: b/335700118
Change-Id: I028b0e36e7f629396655c4421cdef93d3803d197
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5464670


Commit-Queue: Hailey Wang <haileywang@google.com>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1289607}