Eliminate move_it macros

[brson]

These are scattered around from an era when match move did not work.

[bblum]

One that I was not able to get rid of with a localized fix is the last one remaining in pipes.rs - in a destructor, it moves out of a field of the struct. I considered using the option dance, but I remember also thinking it might be fixable as soon as #3224 is fixed.

[thestinger]

@bblum: it seems that could be fixed if #4330 is implemented

[bblum]

That's true.

[nikomatsakis]

Not critical for 0.6; de-milestoning

[nikomatsakis]

Still relevant as of today. See comment in #4330
regarding discussion from today's meeting.

[emberian]

The only place this still exists is the pingpong benchmark, closing.