docs: remove "--" from the default value of 'quotestr'

Adjust the documentation to the removal of "--" in the previous commit.

doc/nano.1

@@ -142,7 +142,7 @@ and place it at that position again upon reopening such a file.
 .TP
 .BR "\-Q ""\fIregex\fB""" ", " "\-\-quotestr=""" \fIregex """
 Set the regular expression for matching the quoting part of a line.
-The default value is \fB"^([\ \\t]*([!#%:;>|}]|//|\-\-))+"\fP.
+The default value is \fB"^([\ \\t]*([!#%:;>|}]|//))+"\fP.
 (Note that \fB\\t\fP stands for an actual Tab.)
 This makes it possible to rejustify blocks of quoted text when composing
 email, and to rewrap blocks of line comments when writing source code.

doc/nano.texi

@@ -240,7 +240,7 @@ and place it at that position again upon reopening such a file.
 @item -Q "@var{regex}"
 @itemx --quotestr="@var{regex}"
 Set the regular expression for matching the quoting part of a line.
-The default value is @t{"^([@w{ }\t]*([!#%:;>|@}]|//|--))+"}.
+The default value is @t{"^([@w{ }\t]*([!#%:;>|@}]|//))+"}.
 (Note that @code{\t} stands for a literal Tab character.)
 This makes it possible to rejustify blocks of quoted text when composing
 email, and to rewrap blocks of line comments when writing source code.
@@ -872,7 +872,7 @@ keystroke instead of 25.  Note that @option{constantshow} overrides this.
 
 @item set quotestr "@var{regex}"
 Set the regular expression for matching the quoting part of a line.
-The default value is @t{"^([@w{ }\t]*([!#%:;>|@}]|//|--))+"}.
+The default value is @t{"^([@w{ }\t]*([!#%:;>|@}]|//))+"}.
 (Note that @code{\t} stands for a literal Tab character.)
 This makes it possible to rejustify blocks of quoted text when composing
 email, and to rewrap blocks of line comments when writing source code.

doc/nanorc.5

@@ -219,7 +219,7 @@ keystroke instead of 25.  The option \fBconstantshow\fR overrides this.
 .TP
 .BI "set quotestr """ regex """
 Set the regular expression for matching the quoting part of a line.
-The default value is "\fB^([\ \\t]*([!#%:;>|}]|//|\-\-))+\fP".
+The default value is "\fB^([\ \\t]*([!#%:;>|}]|//))+\fP".
 (Note that \fB\\t\fR stands for an actual Tab character.)
 This makes it possible to rejustify blocks of quoted text when composing
 email, and to rewrap blocks of line comments when writing source code.

doc/sample.nanorc.in

@@ -125,7 +125,7 @@
 
 ## The regular expression that matches quoting characters in email
 ## or line-comment introducers in source code.  The default is:
-# set quotestr "^([ 	]*([!#%:;>|}]|//|--))+"
+# set quotestr "^([ 	]*([!#%:;>|}]|//))+"
 
 ## Try to work around a mismatching terminfo terminal description.
 # set rawsequences