remove unnecessary initializations

[jc: I needed to hand merge the changes to the updated codebase,
 so the result needs to be checked.]

Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/builtin-update-index.c b/builtin-update-index.c
index d2556f3..9f0cf28 100644
--- a/builtin-update-index.c
+++ b/builtin-update-index.c
@@ -23,7 +23,7 @@
 static int info_only;
 static int force_remove;
 static int verbose;
-static int mark_valid_only = 0;
+static int mark_valid_only;
 #define MARK_VALID 1
 #define UNMARK_VALID 2