Revert "ANDROID: fscrypt: add key removal notifier chain"

This reverts commit 98261f39
because it was only needed for sdcardfs, which has now been removed.

Bug: 157700134
Bug: 142275883
Change-Id: Iaf22521ef47d48ce9c9c0604a8b2412e3b8c1faa
Signed-off-by: Eric Biggers <ebiggers@google.com>