[FEATURE composable-computed-properties] Fix another CCP bug.

`normalizeDependentKey` had a typecheck, but it shouldn't really care about the
non-cp case.  More importantly, the typecheck didn't check for booleans so
things like `Em.computed.equal('isThisTypeCheckWorking', false)` would error.
Merge pull request #4209 from hjdivad/fix-ccp-stupid-typecheck

[FEATURE composable-computed-properties] Fix another CCP bug.