Moves Endpoint from libtock to API (#598)

The main benefit is that we removed all mentions of "tock" from all
source code that is not `main.rs` or inside `env/`.

This change makes libtock-drivers oblivious to how many endpoints are
supported. The endpoint is now checked a bit later in the stack.

third_party/libtock-drivers/Cargo.toml

@@ -13,6 +13,5 @@ libtock_core = { path = "../../third_party/libtock-rs/core" }
 
 [features]
 debug_ctap = []
-vendor_hid = []
 verbose_usb = ["debug_ctap"]
 with_nfc=[]