Revert "Enable IMS#canImeRenderGesturalNavButtons() by default (2nd try)"

This reverts commit f21d2115 [1].

Reason for revert:
IME Nav buttons are unexpectedly invisible in the following cases.
 * work profile apps (Bug 219604375)
 * setup wizard (Bug 218322263)

 [1]: I39f454a2d41d7d5255b8cc4f7d9a3f7a7642b2f3

Bug: 215545985
Fix: 219604375
Test: Manually verified as follows.
 1. Build aosp_coral-userdebug and flash it.
 2. adb install -r TestDPC-normalv8001.apk
 3. Set up work-profile
 4. Enable gestural navigation mode
 5. adb shell am start --user 10 -n \
     com.android.documentsui/com.android.documentsui.files.FilesActivity
 6. Tap the magnifier icon to show the AOSP Keyboard
 7. Confirm that the back button is shown on the nav bar
 8. adb shell dumpsys input_method | grep mNavigationBarController
    -> "No-op implementation"
Change-Id: If3da8dbad0b8bd204cc4ec04f882e9248439c456