adb: warn on remount if undoing deduplication is impossible

A deduplicated filesystem might not have enough free space to undo its
block sharing. In this case "adb remount" should give a more precise
error message.

Bug: 64109868
Test: adb remount on deduplicated filesystem with no free space
Change-Id: I2beb67aa3dfc807cb8493b9c622e7b14174dc9c6