gitk: Remove unused $cdate array

It was unused since commit 9f1afe05c3 ("gitk: New improved gitk").

Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/gitk b/gitk
index 4cde0c4..fec07d3 100755
--- a/gitk
+++ b/gitk
@@ -1621,7 +1621,7 @@
 }
 
 proc parsecommit {id contents listed} {
-    global commitinfo cdate
+    global commitinfo
 
     set inhdr 1
     set comment {}
@@ -1671,9 +1671,6 @@
 	}
 	set comment $newcomment
     }
-    if {$comdate != {}} {
-	set cdate($id) $comdate
-    }
     set commitinfo($id) [list $headline $auname $audate \
 			     $comname $comdate $comment]
 }