phabricator: unconditionally pop `test_vcr` to fix debugcallconduit
11592ce6a711 / D8525 accidentally broke debugcallconduit in non-test scenarios
because it stopped popping `test_vcr` from `kwargs` unconditionally, so when
`--test-vcr` isn't set the empty string still gets passed down as the value of
`test_vcr` in `kwargs`. However unlike all the other commands debugcallconduit
doesn't have an `**opts` argument to receive it, so it aborts because of
invalid arguments.
Differential Revision: https://phab.mercurial-scm.org/D8852
phabricator: demonstrate debugcallconduit being broken without --test-vcr
This was accidentally broken by 11592ce6a711 / D8525
Differential Revision: https://phab.mercurial-scm.org/D8851