CLEANUP: Do not use a fixed type for 'sizeof' in 'calloc'

Changes performed using the following coccinelle patch:

    @@
    type T;
    expression E;
    expression t;
    @@

    (
      t = calloc(E, sizeof(*t))
    |
    - t = calloc(E, sizeof(T))
    + t = calloc(E, sizeof(*t))
    )

Looking through the commit history, grepping for coccinelle shows that the same
replacement with a different patch was already performed in the past in commit
02779b6263a177b1e462e53db6eaf57bcda574bc.
diff --git a/src/uri_auth.c b/src/uri_auth.c
index 57dbadb..27cb66e 100644
--- a/src/uri_auth.c
+++ b/src/uri_auth.c
@@ -226,7 +226,7 @@
 		return NULL;
 
 	if (!u->userlist)
-		u->userlist = calloc(1, sizeof(struct userlist));
+		u->userlist = calloc(1, sizeof(*u->userlist));
 
 	if (!u->userlist)
 		return NULL;