chore(dtslint): refine test descriptions (#4189)
chore(dtslint): refine test descriptions (#4189)

Generic functions are never returned, as doing so is unsafe. The test
descriptions have been changed to better reflect what's tested.
ReactiveX/RxJS,ReactiveX/rxjs,martinsik/rxjs,Brocco/RxJS,Brocco/RxJS,ReactiveX/RxJS,trxcllnt/RxJS,trxcllnt/RxJS,trxcllnt/RxJS,ReactiveX/rxjs,benlesh/RxJS,martinsik/rxjs,kwonoj/RxJS,ReactiveX/RxJS,ReactiveX/rxjs,martinsik/rxjs,ReactiveX/rxjs,benlesh/RxJS,kwonoj/RxJS,trxcllnt/RxJS,benlesh/RxJS,kwonoj/RxJS,martinsik/rxjs,kwonoj/RxJS,Brocco/RxJS,Brocco/RxJS,ReactiveX/RxJS,benlesh/RxJS