DEV: coccinelle: Remove unused `expression e`

Introduced in ef00c533e1ed37b414aab912f492be794ab589cc.
diff --git a/dev/coccinelle/ist.cocci b/dev/coccinelle/ist.cocci
index 97ce0a2..598ffa3 100644
--- a/dev/coccinelle/ist.cocci
+++ b/dev/coccinelle/ist.cocci
@@ -31,7 +31,6 @@
 
 @@
 struct ist i;
-expression e;
 @@
 
 - i.ptr++;