Change /data to tmpfs

For security reason, we will use tmpfs for /data. It should contain only
small, temporary files for now.

vold is removed as it's redundant now. MicrodroidTestCase's boot marker
is also updated because logd reinit won't happen if vold is removed.

Bug: 185767624
Test: atest MicrodroidHostTestCases
Change-Id: I3f60d5dfad2519b6d593a3f514bb50c50019b526
7 files changed