Remove allow_network_time_update_service flag

Test: manual
1. Turn off Bluetooth and cellular
2. Ensure watch is connected to WiFi
3. adb shell device_config put wear_systems com.google.android.clockwork.settings.flags.revamp_time_sync true
4. adb shell device_config put wear_systems android.server.allow_network_time_update_service true

5. adb shell settings put global tethered_config_state 2
6. adb reboot
7. turn off auto time detection
8. change the time on the watch
9. turn on auto time detection
10. Watch should switch to the current time
11. adb shell cmd network_time_update_service dump
12. network_time_update_service dump NtpTrustedTime should have most recent time suggestion
13. adb shell cmd time_detector dump
14. Network suggestion history should have most recent time suggestion

Flag: EXEMPT flag removal
Bug: 424405367
(cherry picked from https://partner-android-review.googlesource.com/q/commit:ade8b44a2e0035a9447749460fc177898181e450)
Merged-In: I5fbb4f51a83378dc42bf3c2a124a2a3bc2c65b83
Change-Id: I5fbb4f51a83378dc42bf3c2a124a2a3bc2c65b83