Remove C++ scheduler

[brson]

Some things blocking it:

• Stack growth
• Select
• Multithreading
• Platform thread Do we really need this?
• 1:1 - May be able to remove it temporarily. Alternately use task pinning and scheduler policy as a temporary until true thread tasks work.

[thestinger]

Visiting for triage, this seems to be very close to happening.

[emberian]

Closed by #8387 \o/