Switch to fs_mgr_read_fstab("/fstab.device")

fstab.device is for backward compatibility in legacy devices.
As it doesn't have fstab entries in device tree (for early mount) so we
can just use the ordinary fs_mgr_read_fstab().

For new devices having early mount, it should use
fs_mgr_read_fstab_default() instead.

Bug: 35811655
Test: adb reboot sideload && adb sideload ota.zip

Change-Id: I00b56a39747ab46d0e87da3c79b9f9faf0d1daef
(cherry picked from commit eb895c90)