Update string for editing an insecure VPN.

The new string comes from the connectivity s strings document: https://screenshot.googleplex.com/9nQFc9PFwgCYCFV
Test: atest -c SettingsUnitTests
Bug: 176821216
Bug: 184921649

Change-Id: I76257a4a2c2b9d5a49248296676d98980be9d77c
Merged-In: I76257a4a2c2b9d5a49248296676d98980be9d77c
(cherry picked from commit ec4b6129)