aconfig: rename test flag `disabled_rw_2` -> `disabled_rw_in_other_namespace`

The flag `disabled_rw_2` is used to verify that aconfig can
auto-generate code for flags in different namespaces. Rename the flag to
`disabled_rw_in_other_namespace` to highlight that it belongs to a
different namespace than the other flags.

This CL is a semantic change only.

Bug: None
Test: atest aconfig.test
Change-Id: Ib82fdce0ca3f7cd56b9b3f80e44fe424a03a2ae4