aflags: list: merge package and name into fully qualified name

Print the fully qualified name instead of splitting flag package and
flag name into separate columns. This aligns the output with the
expected input to `aflags enable <fully-qualified-name>` and makes it
easier to copy-and-paste the flag names.

Before this change:

  $ adb shell aflags list | head -n4
  android.app.admin.flags                   cross_user_suspension_enabled                                              false default read-write system
  android.app.admin.flags                   dedicated_device_control_enabled                                           false default read-write system
  android.app.admin.flags                   device_policy_size_tracking_enabled                                        false default read-write system
  android.app.admin.flags                   dumpsys_policy_engine_migration_enabled                                    false default read-write system

After this change:

  $ adb shell aflags list | head -n4
  android.app.admin.flags.cross_user_suspension_enabled                                                           false default read-write system
  android.app.admin.flags.dedicated_device_control_enabled                                                        false default read-write system
  android.app.admin.flags.device_policy_size_tracking_enabled                                                     false default read-write system
  android.app.admin.flags.dumpsys_policy_engine_migration_enabled                                                 false default read-write system

Bug: N/A
Test: adb shell aflags list
Change-Id: I3227c9c9c7355b5b0c1b75ada73b1a8f87d1be55