`main()` function used to be needed to support dart, since dart
Does not allow top level statements. Since we no longer use dart
The need for `main()` has been removed.
In preparation for `Basel` and standardized way of running tests
we are removing `main()`
PR Close#21053
`flush()` can now be used from within fakeAsync tests to simulate moving
time forward until all macrotask events have been cleared from the
event queue.
Miško Hevery
Julie Ralph
Jason Aden