ErrorProne: BluetoothKeystoreService

In btservice/bluetoothKeystore/BluetoothKeystoreService.java:
```
576: warning: Private method 'readChecksumFile' is never used.
    private void readChecksumFile([...]) throws IOException {
                 ^
95: warning: The field 'CONFIG_FILE_CHECKSUM_PATH' is never read.
    private static final String CONFIG_FILE_CHECKSUM_PATH =
                                ^
97: warning: The field 'CONFIG_BACKUP_CHECKSUM_PATH' is never read.
    private static final String CONFIG_BACKUP_CHECKSUM_PATH =
                                ^
452|453: warning: It is very rare for LinkedList to out-perform ArrayList or ArrayDeque.
Avoid it unless you're willing to invest a lot of time into benchmarking.
Caveat: LinkedList supports null elements, but ArrayDeque does not.
        List<String> configEncryptedLines = new LinkedList<>();
                                            ^
557: warning: StringBuffer performs synchronization that is usually unnecessary;
prefer StringBuilder.
                StringBuffer hashString = new StringBuffer();
                                          ^
732: warning: Parameter name `data` is unknown.
     * @param data String as base64 to be decrypted.
       ^
```

Bug: 236759221
Test: m RUN_ERROR_PRONE=true Bluetooth
Change-Id: Ic5ff3df5391ef4596b1ba15a78485d532385851c