chore: Remove watch alias in favor of standard grunt-karma syntax

The README for grunt-karma recommends executing watch tasks in a single Grunt
command using the form `$ grunt karma:server watch`. I am removing the
`watch:karma` alias in favor of this more explicit invokation to prevent
confusion with an (implied but nonexistent) "karma" target for the watch task.
To further clarify what's happening during watch, the watch task's settings
have been moved into a "test" task target.