match: delete unused argument "listsubrepos" from _buildmatch()
Seems to have been unused since
9f9ffe5f687c (match: compose 'set:'
pattern as matcher, 2018-06-10).
Differential Revision: https://phab.mercurial-scm.org/D5924
match: delete unused rel() (API)
Differential Revision: https://phab.mercurial-scm.org/D5923