remove transient fields from migration task hashCode() and equals()

[fil512]

e.g. We need to remove both myIsOkayIfNeitherColumnExists and
myDeleteTargetColumnFirstIfBothExist from RenameColumnTask.hashCode() and RenameColumnTask.equals().

Only those fields directly pertinent to what's being migrated should be included in the hashCode. Flyway uses this hashCode to validate the migration hasn't been "tampered with" since it was last run.

[jamesagnew]

ooh good call.

I guess we should get a rush on this since it will be a nuisance to implement once 4.2.0/2020.02 are out.

[fil512]

Thanks for doing this @jaferkhan !

[jaferkhan]

@fil512 You're most welcome ^_^