store: remove unneeded depedency

Author: tilacog

store/postgres/Cargo.toml

@@ -38,7 +38,6 @@ hex = "0.4.3"
 [dev-dependencies]
 clap = "2.33.3"
 graphql-parser = "0.3"
-hex = "0.4.3"
 test-store = { path = "../test-store" }
 hex-literal = "0.3"
 graph-mock = { path = "../../mock" }