Remove TestRandom (#9006)

We  have a legacy `TestRandom` trait which generates random types for testing and fuzzing.
This function overlaps with `arbitrary` which is used very commonly in the ecosystem.


  Remove `TestRandom` and generate random type instances using `Arbitrary`.


Co-Authored-By: Mac L <mjladson@pm.me>

Co-Authored-By: Michael Sproul <michael@sigmaprime.io>

consensus/state_processing/Cargo.toml

@@ -37,7 +37,6 @@ rayon = { workspace = true }
 safe_arith = { workspace = true }
 smallvec = { workspace = true }
 ssz_types = { workspace = true }
-test_random_derive = { path = "../../common/test_random_derive" }
 tracing = { workspace = true }
 tree_hash = { workspace = true }
 typenum = { workspace = true }
@@ -45,4 +44,5 @@ types = { workspace = true }
 
 [dev-dependencies]
 beacon_chain = { workspace = true }
+state_processing = { path = ".", features = ["arbitrary"] }
 tokio = { workspace = true }