Do not document path to be repeatable in apt-ftparchive cmds

The manpage for apt-ftparchive {packages,sources} claims that the
path argument can be repeated, but that logically conflicts with having
two optional arguments after that and isn't implemented in code either,
so we just adapt the documentation to reality here.

So, since when is this documentation wrong? The manpage is currently
written in xml (since 2004), but the sgml before that had the same
mistake included all the way back to a time in which time itself is not
stable (the commit is dated in git 2004, but the commit message
says 2001 while including a d/changelog stanza dated 2000) in
my favorite commit "Join with aliencode" which brought in a whole lot
of stuff adding also (quoting said d/changelog entry) "apt-ftparchive
the all dancing all singing FTP archive maintenance program".

In other words: It was documented this way for more than 22 years.

Reported-By: Michael Tokarev on IRC

debian/changelog

@@ -11775,7 +11775,7 @@ apt (0.5.0) unstable; urgency=low
   * Ability to parse and return source index build depends from Randolph.
   * new 'apt-get build-dep' command from Randolph. Closes: #63982
   * Added apt-ftparchive the all dancing all singing FTP archive
-    maintinance program
+    maintenance program
   * Allow version specifications with =1.2.4-3 and /2.2 or /stable postfixes
     in apt-get.
   * Removed useless internal cruft including the xstatus file.

doc/apt-verbatim.ent

@@ -403,7 +403,7 @@
 	<arg choice='plain' rep='repeat'>&synopsis-param-filename;</arg>
 	&synopsis-help;
 </cmdsynopsis></refsynopsisdiv>">
-<!ENTITY synopsis-arg-ftparchive "<arg choice='plain' rep='repeat'><replaceable>&synopsis-path;</replaceable></arg><arg><filename><replaceable>&synopsis-override;</replaceable></filename><arg><replaceable>&synopsis-pathprefix;</replaceable></arg></arg>">
+<!ENTITY synopsis-arg-ftparchive "<arg choice='plain'><replaceable>&synopsis-path;</replaceable></arg><arg><filename><replaceable>&synopsis-override;</replaceable></filename><arg><replaceable>&synopsis-pathprefix;</replaceable></arg></arg>">
 <!ENTITY synopsis-command-apt-ftparchive "<refsynopsisdiv><cmdsynopsis>
 	<command>apt-ftparchive</command>
 	<arg><option>-dsq</option></arg>