Fix a condition to reset the current spell checker

TextServicesManagerService has had a logic to reset
Settings.Secure.SELECTED_SPELL_CHECKER when the current spell checker
service is uninstalled, but it had not been working until we fixed a
bug that had prevented that logic from running [1].  However, there
has been another bug in that logic itself that resets
Settings.Secure.SELECTED_SPELL_CHECKER also when the current spell
checker service APK is updated.

With this CL, Settings.Secure.SELECTED_SPELL_CHECKER will be reset
only when the package disappears, not when it is just being replaced
with a new APK.

 [1]: I30902a3d94f2ddef33f4a8067799e98322ae3a03
      34a04e40

Fix: 79110151
Test: Manually verified as follows.
      1. adb install -r SampleSpellCheckerService.apk
      2. adb shell settings get secure selected_spell_checker
        -> com.android.inputmethod.latin/.spellcheck.AndroidSpellCheckerService
      3. adb shell "settings put secure selected_spell_checker 'com.example.android.samplespellcheckerservice/.SampleSpellCheckerService'"
      4. adb shell settings get secure selected_spell_checker
        -> com.example.android.samplespellcheckerservice/.SampleSpellCheckerService
      5. adb install -r SampleSpellCheckerService.apk
      6. adb shell settings get secure selected_spell_checker
        -> com.example.android.samplespellcheckerservice/.SampleSpellCheckerService
Test: Manually verified that Bug 67412078 is still fixed.
Change-Id: Ic07fc2f418f051b2825d993fa959ed36f9b0f3c7