Revert "Fix the accessibility shortcut funtionaility."

This reverts commit 72c52dfb.

Reason for revert: The original commit only changed what was displayed in the settings, but not the actual value of the setting that was used during the shortcut operation.

Bug: b/269693551
Test: Locally tested on adt4-userdebug that the shortcut does not show TalkBack as target service if it is set to an empty string and the settings are opened for the very first time.

Change-Id: Ife2e098d1e55ed94efb2426505872546b27bc3bb