Remove Settings constants for NetworkStack

The definitions reference of these constants are moved from
Settings to DeviceConfig. These definitions are @hide and the
usage in the Settings are removed. Thus, remove the definitions
from API level.

Bug: 123167629
Test: make system-api-stubs-docs-update-current-api \
      test-api-stubs-docs-update-current-api
Test: atest NetworkStackTests
Change-Id: I28c4bf2c0b72e154cea91d11007a9497c7f21570
Merged-In: I7291cfa86cd6e907df35e8fbc97e2e9a77e56cab
Merged-In: Ic48bea07e79490dd3787068bc88c748525752a61