Remove supportsDismissingSelfWindow attribute of IME

This partially reverts CL I0f6b130a7df57557e40b52a7b7ac00be965a17c3.

Fixes: 34133139
Test: Confirm that unit test passed.
    adb install out/target/product/.../data/app/FrameworksCoreTests/FrameworksCoreTests.apk
    adb shell am instrument -w \
        -e class android.view.inputmethod.InputMethodInfoTest \
        com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner
Change-Id: I2b94263b2a0bf330bf9973567fea2d35176754d7