sysutils/rsyslog8: delete unnecessary code

Remove USE_LDCONFIG -- the port installs a number of loadable modules
for its own use. These are not shared libraries that ldconfig(8)
needs to deal with. (1)

Remove REINPLACE_CMD lines that no longer do anything. The library
path compiled into the code is set from autoconfig nowadays.

PR: 262393 (1)
Reported by: mikael