You shouldn’t need RW7 to open a RW7 project in RW8. I have both so I haven’t tried this, but should be easy enough to test. Just move the RW7 program from your application folder to the trash and open a RW7 project.
I would keep RW7 in case you have any issues upgrading a project (unlikely but you never know) To open a RW 7 project in RW7, drag it to the RW7 Icon or make sure that RW8 app is closed.