Rename language codes sr-ec and sr-el to sr-cyrl and sr-latn
sr-ec and sr-el are not conform to BCP 47.
BCP 47 explicit mentions sr-Latn and sr-Cyrl as examples.
Bug: T117845
Depends-On: I666fbdea89ccf21aab6ca1849adf22813dec052e
Change-Id: Ia1ec2bfe1309964220acc4d46e134717f21b7029