alembic: Remove batch operations (and sqlite support)

Because SQLite doesn't support full ALTER capabilities, alembic scripts
require batch operations.  However, that capability wasn't available until
0.7.0 which some distributions haven't reached yet.  Therefore, the batch
operations introduced in commit 86d6e44c (review 2319) have been reverted
and SQLite is unsupported again, for now anyway.

Tested the full upgrade and downgrade on MySQL/Mariadb and Postgresql.

ASTERISK-25890 #close
Reported-by: Harley Peters

Change-Id: I82eba5456736320256f6775f5b0b40133f4d1c80