doc: formatting fixes in "du.x" and "rm.x"

Avoid warnings from: groff -b -e -mandoc -T utf8 -rF0 -t -w w -z

* man/du.x: Change ".BR" to ".B" if there is only one argument.
Protect an end-of-sentence indicator (.?!) with '\&'
if it does not mean an end of a sentence.
Change '--' to '\-\-' if it indicates an option.
* man/rm.x: Change '\=' to '='.

man/du.x

@@ -9,20 +9,20 @@ du \- estimate file space usage
 .\" Add any additional description here
 [PATTERNS]
 PATTERN is a shell pattern (not a regular expression).  The pattern
-.BR ?
+.B ?\&
 matches any one character, whereas
-.BR *
+.B *
 matches any string (composed of zero, one or multiple characters).  For
 example,
-.BR *.o
+.B *.o
 will match any files whose names end in
 .BR .o .
 Therefore, the command
 .IP
-.B du --exclude=\(aq*.o\(aq
+.B du \-\-exclude=\(aq*.o\(aq
 .PP
 will skip all files and subdirectories ending in
-.BR .o
+.B .o
 (including the file
-.BR .o
+.B .o
 itself).

man/rm.x

@@ -13,7 +13,7 @@ documents the GNU version of
 removes each specified file.  By default, it does not remove
 directories.
 .P
-If the \fI\-I\fR or \fI\-\-interactive\=once\fR option is given,
+If the \fI\-I\fR or \fI\-\-interactive=once\fR option is given,
 and there are more than three files or the \fI\-r\fR, \fI\-R\fR,
 or \fI\-\-recursive\fR are given, then
 .B rm
@@ -22,7 +22,7 @@ the response is not affirmative, the entire command is aborted.
 .P
 Otherwise, if a file is unwritable, standard input is a terminal, and
 the \fI\-f\fR or \fI\-\-force\fR option is not given, or the
-\fI\-i\fR or \fI\-\-interactive\=always\fR option is given,
+\fI\-i\fR or \fI\-\-interactive=always\fR option is given,
 .B rm
 prompts the user for whether to remove the file.  If the response is
 not affirmative, the file is skipped.