doc: clean up manpage description of "notmuch-config list" output

The escaping in the description of the output of "notmuch-config list"
appears to have been inherited from some previous attempts at
documentation.  It leaked out in the actual generated manpage
documentation, where it looks like this:

       list   Every  configuration  item is printed to stdout, each on a
              separate line of the form:

                 *section*.\ *item*\ =\ *value*

This simplification cleans up the overescaping.

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>

doc/man1/notmuch-config.rst

@@ -38,7 +38,7 @@ programmatically as described in the SYNOPSIS above.
     Every configuration item is printed to stdout, each on a separate
     line of the form::
 
-        *section*.\ *item*\ =\ *value*
+        section.item=value
 
     No additional whitespace surrounds the dot or equals sign
     characters. In a multiple-value item (a list), the values are