Documentation/gitdiffcore: Remove misleading date in heading

Ever since the automatic conversion into man form, the heading
contained a misidentified subheading reading "June 2005".
Remove this since the documentation is more recent, and the correct
date is in the footer.
Signed-off-by: NMichael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/gitdiffcore.txt

@@ -3,7 +3,7 @@ gitdiffcore(7)
 
 NAME
 ----
-gitdiffcore - Tweaking diff output (June 2005)
+gitdiffcore - Tweaking diff output
 
 SYNOPSIS
 --------