Rename `libsyn` to `libsyn2`

A downstream project has an invalid branching structure, so we can't
actually rename `libsyn` to `libsyn-legacy` like we normally would.
Instead, we must allow the legacy package to squat on the `libsyn` name
until the branching structure is fixed to unblock the upgrade to
syn-2.x.

Test: TreeHugger
Bug: 276463929
Bug: 278978404
Change-Id: If72d389dd5238299cc1b35818e0b5596b0469cb1
1 file changed