No need to send PRE_BOOT_COMPLETED for new users

Since the primary purpose is to upgrade databases, no need
to send this broadcast. If system apps care to be informed early
on new user creation, USER_INITIALIZE is an early broadcast.

Also remove some logs that spew when switching users.

Bug: 16846465
Change-Id: Ibd7f8630ce1f41f8cadbda616de05844b127d1a8