Disabling extra heap_pages allocation for parachain clients

[crystalin]

Parachain blocks are validated on the relay using a wasmtime executor with fixed heap pages.
However it is possible to change the heap pages using onchain storage

substrate/primitives/state-machine/src/backend.rs

Lines 447 to 452 in f4cb21c

	let heap_pages = self
	.backend
	.storage(sp_core::storage::well_known_keys::HEAP_PAGES)
	.ok()
	.flatten()
	.and_then(|d| codec::Decode::decode(&mut &d[..]).ok());

I would suggest to remove the heap pages support for parachain, preventing the case where a parachain block is produced with a given heap pages count that cannot be executed on the relaychain.

@bkchr What do you think ?

[bkchr]

I had though that I already had written an issue for it, but I was wrong :P

Here it is now: https://github.com/paritytech/cumulus/issues/2641

[crystalin]

Sorry forgot to search also in cumulus :(

[bkchr]

Haha, the issue didn't existed before you asked :D