Revert "[Thread] add Android.bp for Thread flags"

This reverts commit a59a6e30.

Reason for revert: this should not be added in the mainline module but in platform

Merged-In: I88c993680976d2e10d672bfdbf45119f2db13868
Change-Id: I680f23b5f8099b1ea4a316b768a56f1be5c78862