[rails6][GuestDevice] Support `present` column
[rails6][GuestDevice] Support `present` column

Do to a performance fix in Rails 6:

- https://github.com/rails/rails/commit/cc2d614e

The GuestDevice#present column would cause the application to raise the
following error:

  ActiveRecord::DangerousAttributeError:
    present? is defined by Active Record. Check to make sure that you
    don't have an attribute or method with the same name.

This workaround avoids having to create a database migration to fix this
column, and instead allows us to keep the column we have had in place
for years for a performance fix that doesn't apply to this model anyway.

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