Package /data instead of userdata.img in sdk images

userdata.img becomes 4GB in P and it doesn't work well with patcher in
android studio. We decided to remove userdata.img in system image zip
and generate userdata.img from /data by emulator.
Within the /data folder, we only keep /misc for the emulated WiFi.
This cl does not impact real devices.

BUG: 79925096

Change-Id: Ida3f2163cab30b38cd02a0280b5fd7abd9a66945
Signed-off-by: Weilun Du <wdu@google.com>