releasetools: Drop the support for BBOTA v1 and v2.

BBOTA v1 and v2 (introduced in L and L MR1 respectively) don't support
resumable OTA. We shouldn't generate packages using v1/v2 at the risk of
bricking devices.

BBOTA v3 (since M) and v4 (since N) both support resumable OTAs. BBOTA
v4 additionally supports using FEC to possibly recover a corrupted
image.

Bug: 33694730
Test: Generate full and incremental OTAs w/ and w/o the CL. They should
      give identical packages (in v4).
Change-Id: Ib89d9cd63ba08e8e9aa4131bed18876b89d244c0