Remove key_ prefix from CarrierConfig Strings

Remove the key_ prefix from the resolved string
of:
KEY_SUBSCRIPTION_GROUP_UUID_STRING; and
KEY_IS_OPPORTUNISTIC_SUBSCRIPTION_BOOL

Bug: 130374824
Test: compilation (trivial string change)
Merged-In: I1ae1df9d33229d3f3aba237d865ceb2373761af4
Change-Id: I1ae1df9d33229d3f3aba237d865ceb2373761af4
(cherry picked from commit bbb8968e54707beb893ba23c38667173c072d1a5)