Remove timer code from scheduler

[brson]

The scheduler includes periodic timer wakeups that probably don't do anything useful now (were once for preemption). Let's give them the boot.

[brson]

16:55 <@graydon> brson: actually yeah, my bet is on the WaitForSingleObject(thread, INFINITE) in the bottom of rust_timer.cpp
16:55 <@graydon> just delete that file and any uses of it. it's a disaster and we'll do better once we have Real Timers And Stuff from uv
16:55 <@graydon> I'm ashamed to have written it

[brson]

After looking into this, rust_timer.cpp was dead code, so I removed it. The scheduler is currently using a timed_wait on a condition variable because the signals to the condition variable don't always wake the scheduler (they are not always done while the lock is held). I'm trying to fix this now and remove the timed_wait() function.

[brson]

Currently the scheduler needs to periodically wake up whenever there are running tasks that are yielding to check whether the yield has timed out.

[brson]

I don't know why we need the yield(time) version currently, but I would like to pursue just completely getting rid of the timer version of yield, so that yield does nothing but yield control to the scheduler. When we get uv bindings we can use their timers.

[brson]

Done.