Update mobile data off string to "Mobile data won't autoconnect"

mobile_data_off_summary should be changed from "Internet won't
autoconnect" to "Mobile data won't autoconnect"

Bug: 197935764
Test: build, manual verification that mobile data off summary in
internet dialog is correct

Change-Id: I381a514702387b5c530296b2c909dc6496680f3e
(cherry picked from commit af0171cd)
Merged-In: I381a514702387b5c530296b2c909dc6496680f3e