[1.6.x] Cleaned up a note in docs/topics/db/sql.txt.

Backport of 34a06d99e0fc96a0f0648bfde141d342e963e971 from master
[1.6.x] Fixed #23965 -- Mentioned that FieldFile inherits from File

Backport of 5281d9620d13386fd4403f7aa6b9a2afd9b5a93f from master