cleanup: say goodbye to manifestv2 format
This experiment was a bust: we'd hoped for smaller repository sizes,
but things got larger. Google ended up rolling out tree manifests in a
format that's compatible with the original manifest format, and I
believe Facebook is doing the same. This code was never implemented as
native speedups, so I'm pretty comfortable saying nobody is using the
experimental feature. Let's rip it out.
I noticed this code still kicking around because I was investigating a
repo corruption issue for timeless.
.. bc::
Support for the experimental manifestv2 format has been removed, as
it was never completed and failed to meet expectations.
Differential Revision: https://phab.mercurial-scm.org/D2393
#require docutils gettext
$ $TESTDIR/check-gendoc fr
checking for parse errors