Revert "Adds command-line flag for migration tablename."

This reverts commit 9e548378df5f6a0ef4f09c45ff9c643b15cc5d70.
Revert "Puts migration table in a variable."

This reverts commit 7d0c84f66c7bd8f614ae9c2875632a0308eec201.
Allows setting migration table by environment var.