Removing do keyword from librustdoc
Removing do keyword from libstd and librustc
Remove do keyword from librustuv
Removing do keyword from libnative
Removing do keyword from librustpkg
Removing do keyword from libextra
Removing do keyword from libgreen
Remove do keyword from test/
Remove do keyword from compiletests
Removing usage of the do keyword from documentation
Removing support for the do syntax from libsyntax and librustc.

Fixes #10815.
auto merge of #11868 : bytbox/rust/remove-do, r=cmr

Fixes #10815.