Deprecate /mnt/sdcard -> /storage/self/primary symlink.

"This symlink was suppose to have been removed in the Gingerbread
time frame, but lives on."
https://android.googlesource.com/platform/system/core/+/d2f0a2c%5E!/

Apps targeting R+ must NOT use that symlink.

For older apps we allow core init.rc to create
/mnt/sdcard -> /storage/self/primary symlink.

Bug: 129497117
Test: boot device, /mnt/sdcard still around.
Change-Id: I6ecd1928c0f598792d9badbf6616e3acc0450b0d
7 files changed