vboot: remove fwlib2x, fwlib20, fwlib21 targets

All vboot "versions" are being coalesced into one, accessible via
the vboot_fw.a library, which is built by the fwlib target.

BUG=b:124141368, chromium:968464
TEST=make clean && make runtests
BRANCH=none

Change-Id: I9ea7f067c9ac732eff7e63aa49e5303b340ede8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1961714
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
1 file changed