Remove useless reference to RxJS

This reference is not needed and is now causing problem because the
definitelyTyped for RxJS is now part of the RxJS package directly.  The
Nuget package will needed to be changed also.
Revert "Remove useless reference to RxJS"

This reverts commit dc4d81a6bda11013ce1e1752a53a8cf00606adfd.
Removed useless reference to RxJS typing

Since the typing is now part of RxJS, referencing it (which is causing a
nuget package dependency) will cause a problem by having twice the save
references in the samme app.
Merge pull request #2537 from carldebilly/master

Remove useless reference to RxJS definitions