StorageManager: remove old isFileEncrypted* methods

StorageManager#isFileEncryptedNativeOnly() and
StorageManager#isFileEncryptedNativeOrEmulated() are no longer used,
except for @UnsupportedAppUsage.  However, a clear public API equivalent
exists: StorageManager#isEncrypted(File) can be used to check whether
the device is encrypted.  Since Android 13, file encryption is the only
supported encryption type.  Therefore, these methods can be removed.

Bug: 232458753
Test: presubmit
Change-Id: I3f3707aa54821269201b05a0cdd2a2cdf23b0c9a