Retire the emulator_car_x86_64 board

`rgrep emulator_car_x86_64 --include=*.mk` says
it is not used.

Bug: 295259752
Test: presubmit
Change-Id: Ic0957a426d9cd3161f0a13e651c82717de01f90f
Signed-off-by: Roman Kiryanov <rkir@google.com>
1 file changed