add some mandoc pages and fix some warnings

- add .Os, it is mandatory.
- don't redeclare .Nm when it's not needed.
- fix some warnings (checked with mandoc -Tlint).
- remove some leftover old stuff.

logger.1

@@ -5,7 +5,7 @@
 .Nm logger
 .Nd make entries in the system log
 .Sh SYNOPSIS
-.Nm logger
+.Nm
 .Op Fl is
 .Op Fl p Ar priority
 .Op Fl t Ar tag
@@ -15,7 +15,6 @@
 provides a shell command interface to the
 .Xr syslog 3
 system log module.
-.Pp
 .Sh OPTIONS
 .Bl -tag -width xxxxxxxxxxxx
 .It Fl i