Revert "Revert "Stop dropping caches now we have kernel fix""

This reverts commit 8ad0bef7b5b1b6e1ba3afe441d2dcc9a06e782a7.

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.

Change-Id: I92c7ad0adaa7bd357e10661a47cc667ac0ff84b4
Merged-In: I92c7ad0adaa7bd357e10661a47cc667ac0ff84b4
diff --git a/Ext4Crypt.cpp b/Ext4Crypt.cpp
index 88bedd0..9dfcad8 100644
--- a/Ext4Crypt.cpp
+++ b/Ext4Crypt.cpp
@@ -171,13 +171,6 @@
     LOG(DEBUG) << "Added key " << key_id << " (" << ref << ") to keyring " << device_keyring
                << " in process " << getpid();
 
-    // *TODO* Remove this code when kernel is fixed - see b/28373400
-    // Kernel preserves caches across a key insertion with ext4ice, which leads
-    // to contradictory dirents
-    if (!android::base::WriteStringToFile("3", "/proc/sys/vm/drop_caches")) {
-        PLOG(ERROR) << "Failed to drop_caches";
-    }
-
     return true;
 }