Fixed ApnEditor crash issue

This root caused is that we closed the managed cursor which lifecycle is
managed by Activity.

Actually, we don't need the managed cursor in this case, just use the
normal cursor and close it after we got the apn data from the database.

Bug: 77894798
Test: make ROBOTEST_FILTER=ApnEditorTest -j40 RunSettingsRoboTests
Change-Id: I6eb80bbd53354e00e871e974f520668dcbceac63