Shift stringslint to using python3.

Bug: 169704254
Test: manual
Change-Id: I175bdf75e7424bef6d4ac9f51797510766de2b14
(cherry picked from commit 85ccd0418097d774d8db8af77da2d6b5ed75d743)
Merged-In: I354ef4b12c75505a069fdf657ab98a9b122785c7
2 files changed