Remove FunctionWithParamTokens.
All test wrappers async, fakeAsync and inject now return just a Function instead of FunctionWithParamTokens. This makes them directly consumable by the test framework. Also the test framework code does not have to handle a union of Function and FunctionWithParamTokens everywhere.
The Function returned by the above methods are considered asynchronous by the test framework if they return a Promise, synchronous otherwise.
Closes#8257
