net/xrdp: Adjust the default configuration to FreeBSD

Since xrdp 0.10.2, it supports running xrdp daemon as unpriviled user
(See also UPDATING 20241224).

The user/group to run xrdp daemon is "_xrdp" and will be created
automatically, but "xrdp" is specified with commented out in upstream
default config. This might mislead some users that they need to create
"xrdp" user manually.

PR: 289138