Documentation/rev-list: don't list date formats

We are about to add several new date formats which will make this list
too long to display in a single line.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rev-list.txt

@@ -45,7 +45,7 @@ SYNOPSIS
 	     [ --regexp-ignore-case | -i ]
 	     [ --extended-regexp | -E ]
 	     [ --fixed-strings | -F ]
-	     [ --date=(local|relative|default|iso|iso-strict|rfc|short) ]
+	     [ --date=<format>]
 	     [ [ --objects | --objects-edge | --objects-edge-aggressive ]
 	       [ --unpacked ] ]
 	     [ --pretty | --header ]

Documentation/rev-list-options.txt

@@ -699,7 +699,7 @@ include::pretty-options.txt[]
 --relative-date::
 	Synonym for `--date=relative`.
 
---date=(relative|local|default|iso|iso-strict|rfc|short|raw)::
+--date=<format>::
 	Only takes effect for dates shown in human-readable format, such
 	as when using `--pretty`. `log.date` config variable sets a default
 	value for the log command's `--date` option.