runq: Remove userland references to RQ_PPQ in rtprio contexts
Concerns only a single test (ptrace_test.c).
MFC after: 1 month
Event: Kitchener-Waterloo Hackathon 202506
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D45390
(cherry picked from commit b2a9ee2a72eabcfe7942cfbc2a576b5603ef218c)