meson: don't search PATH for telinit (#7770)

meson: don't search PATH for telinit (#7770)

On a typical system running systemd, the telinit in PATH is very likely to be a symlink
to systemctl. Setting TELINIT to this may result in an infinite recursion if telinit is called
and sd_booted() == 0. This may commonly occur in a chroot environment.

Bug: https://bugs.gentoo.org/642724

[zj:
The path was originally hardcoded as "/lib/upstart/telinit", but was made configurable without
changing the default in 4ad61fd1806dde23d2c99043b4bed91a196d2c82. Then the default was
changed to `/lib/sysvinit/telinit` in abaaabf40a9891014ed4c402d7beb5a67ac256b1. Then it
started being  autodetected when meson support was added in
5c23128daba7236a6080383b2a5649033cfef85c. This patch restores the behaviour that was
implemented in configure.ac at the time of its removal.]