Retire obsolete (32bit-only) emulator targets and boards

Please use 64bit-only targets instead:
* sdk_phone64_x86_64
* sdk_phone64_arm64
* we don't support x86+arm for AOSP targets

Bug: 295259752
Test: presubmit
Change-Id: I887e21ad00e6981a162da5cf1cc47827d068eee7
Signed-off-by: Roman Kiryanov <rkir@google.com>