Remove "Op" "Label" suffixes from enum Label's in Splinter (Rust code)

[tenzinhl]

Note: this issue targets the splinter branch

A style choice. At some point we should remove "-Op" and "-Label" suffixes from labels, because in Rust the labels are already enums and thus namespaced by the name "Label" (as enforced by the state_machine! macro).

An example of this can be found in AbstractMap_v.rs