Remove width restriction on size_in_bytes

The UR update classes from db command (PR #52) appears to have added a standard integer width restriction to this column even though the underlying column type is bigint.

This removes that.
Seems like this is okay as a workaround but maybe we should add BigInt to UR::Value or something?  We want to be able to run `ur update classes-from-db` or whatever in coordination with schema changes and we can't keep track of all these exceptions (we need to fix them instead).