py/runtime: Remove nlr protection when calling __next__ in mp_resume.

And remove related comment about needing such protection when calling send.

Reasoning for removal is as follows:
- mp_resume is only called by the VM in YIELD_FROM opcode
- if send_value != MP_OBJ_NULL then throw_value == MP_OBJ_NULL
- so if __next__ or send are called then throw_value == MP_OBJ_NULL
- if __next__ or send raise an exception without nlr protection then the
  exception will be handled by the global exception handler of the VM
- this handler already has code to handle exceptions raised in YIELD_FROM,
  including correct handling of StopIteration
- this handler doesn't handle the case of injection of GeneratorExit, but
  this won't be needed because throw_value == MP_OBJ_NULL

Note that it's already possible for mp_resume() to raise an exception
(including StopIteration) from the unprotected call to type->iternext(), so
that's why the VM already has code to handle the case of exceptions coming
out of mp_resume().

This commit reduces code size by a bit, and significantly reduces C stack
usage when using yield-from, from 88 bytes down to 40 for Thumb2, and 152
down to 72 bytes for x86-64 (better than half).  (Note that gcc doesn't
seem to tail-call optimise the call from mp_resume() to mp_obj_gen_resume()
so this saving in C stack usage helps all uses of yield-from.)

0 files changed, 0 insertions, 0 deletions