Revert "Stop dropping caches now we have kernel fix"

This reverts commit 6abe6831b59a56145cdd28445cd46fa3c79ecb92.

Bringing this back temporarily for the same issue on sdcardfs.
Will remove once the kernel issue is resolved.

Change-Id: Ia29ea4fddb7777012a2eea9259f9ac856773fe01
Bug: 37231161
Test: Boot device with FBE enabled. ls /storage/emulated/0/Android
Unlock device. ls /storage/emulated/0/Android
1st will not be found. Second should be found.
1 file changed