Fix for warning: unnecessary non-null assertion (!!) on a non-null receiver

Removed multiple instances of unnecessary non-null assertions within the AOSP Calendar app as part of resolving warning messages.

Bug: 237017037

Test: manual testing on bramble device and ran:
adb shell am instrument -w com.android.calendar.tests

With result:
com.android.calendar.FormatDateRangeTest:.
com.android.calendar.UtilsTests:..................
com.android.calendar.WeekNumberTest:.
com.android.calendar.widget.CalendarAppWidgetServiceTest:..
Test results for InstrumentationTestRunner=......................
Time: 0.093

OK (22 tests)

Change-Id: I455b76d79ee1518bb89721099430a0e3e5903faf
(cherry picked from commit 505d6d4d32b2e59964b64f2139c6aa733b0aacbc)
Merged-In: I455b76d79ee1518bb89721099430a0e3e5903faf
9 files changed