Fix invalid use of macros and two typos

It turns out that currently mandoc(1) is not handling Fl in Ss
correctly (maybe it never was). Let's just replace "Fl S \&Ss ..."
with "-S ...". After all, this subsection title is stylized anyway, so Fl
is not that helpful.

MFC after:	2 weeks

usr.bin/env/env.1

@@ -31,7 +31,7 @@
 .\" From FreeBSD: src/usr.bin/printenv/printenv.1,v 1.17 2002/11/26 17:33:35 ru Exp
 .\" $FreeBSD$
 .\"
-.Dd January 19, 2020
+.Dd April 24, 2020
 .Dt ENV 1
 .Os
 .Sh NAME
@@ -165,7 +165,7 @@ and
 .Ar utility
 may not be specified together.
 .\"
-.Ss Details of Fl S \&Ss (split-string) processing
+.Ss Details of -S (split-string) processing
 The processing of the
 .Fl S
 option will split the given
@@ -292,11 +292,11 @@ processing.
 .Pp
 Also,
 .Fl S
-processing can not reference the value of the special parameters
+processing cannot reference the value of the special parameters
 which are defined by most shells.
 For instance,
 .Fl S
-can not recognize special parameters such as:
+cannot recognize special parameters such as:
 .Ql $* ,
 .Ql $@ ,
 .Ql $# ,