bundle2: fix the formatting of the stream part requirements
Use the same pre-encoded normalization as bundlespecs for the stream v2 part
requirements. As it touch the wire protocol, it needs to change before the
release.
This was spotted by Gregory Szorc.
Differential Revision: https://phab.mercurial-scm.org/D1950
#require docutils gettext
$ $TESTDIR/check-gendoc sv
checking for parse errors