cocci: Remove VRT_CTX isomorphism attempt

It does not work, and it is inaccurate since it doesn't include the ctx
identifier that is normally part of the definition (it can't anyway).

Refs f5b0b201

tools/coccinelle/varnish.iso

@@ -13,13 +13,6 @@
 
 /* This section contains VCL types used by VMODs */
 
-Type
-@ vrt_ctx @
-type VRT_CTX;
-@@
-
-VRT_CTX <=> const struct vrt_ctx *
-
 Type
 @ vcl_void @
 type VCL_VOID;