Remove ConfigParser from TextClassificationConstants.

ConfigParser was introduced mostly for reading both legacy Settings and
DeviceConfig lazily. We are ready to migrate to DeviceConfig and no
longer read legacy Settings, and thus we don't need this class.
DeviceConfig invalidates cache whenenver any config in the same namespace
is changed, and thus we don't need a listener.

No performance issue observed after testing TextClassificationManagerPerfTest.

Bug: 143585708
Test: atest FrameworksCoreTests:android.view.textclassifier
Test: atest android.view.textclassifier.cts.TextClassifierServiceSwapTest
Test: frameworks/base/apct-tests/perftests/textclassifier/run.sh
Test: adb shell cmd device_config put textclassifier <key> <value> and
adb shell dumpsys textclassification monitor the value change.
Test: Dynamic switch TCS and make sure the service status is expected.

Change-Id: I3c07ef4b16cd1f81c6aa60a0b9b26cac1a3bb5c0