Cleanup references to the `alloc` dependency

[ra0x3]

• This is old functionality I don't think we need any more
• A simple grep through the code base should do the trick
• Also need to update any docs references to this

[ra0x3]

• After having to revert https://github.com/FuelLabs/fuel-indexer/pull/1367 I think the execution of this is trivial, but the testing is tricky (since it's plugin related)
• I've also updated the issue title from "Remove references" to "Update references", as I think there are several references we can simply remove while still keeping the alloc dependency