Remove KeyStore#state()

Remove AndroidKeyStoreMaintenance#getState() and both overloads of
KeyStore#state().  None of these are used by platform code anymore.

The two KeyStore#state() methods do have @UnsupportedAppUsage, as do two
values of the State enum: UNLOCKED and LOCKED.  However, there is a
clear public API equivalent for apps that may be checking these states:
UserManager#isUserUnlocked().  Therefore, according to the policy on
unsupported usage of internal APIs, we can remove these internal APIs.

Also, the non-SDK dashboard has no runtime results for either method,
and only one static analysis result which is from unused code in one
app.  This is consistent with these methods being entirely unused.

Part of the motivation for removing these internal APIs is that upcoming
changes to the lifetime of keystore superencryption keys would change
the behavior of getState.  So it seems like a good time to remove this
unused/unsupported code instead of wasting time maintaining it.

Bug: 296464083
Test: atest -p --include-subdirs system/security/keystore2
Change-Id: Iff821bbdeac5ee0653c9c71867fd53d38cb4d48f