Remove direct yamux dependency. (#4968)

libp2p-0.16 allows configuring yamux through libp2p-yamux, so the
direct dependency is no longer needed.

While at it we also update to the latest versions of yamux and
nohash-hasher, though the code changes do not depend on it.

substrate/Cargo.lock

@@ -3721,9 +3721,9 @@ checksum = "72ef4a56884ca558e5ddb05a1d1e7e1bfd9a68d9ed024c21704cc98872dae1bb"
 
 [[package]]
 name = "nohash-hasher"
-version = "0.1.3"
+version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "721a2bf1c26159ebf17e0a980bc4ce61f4b2fec5ec3b42d42fddd7a84a9e538f"
+checksum = "2bf50223579dc7cdcfb3bfcacf7069ff68243f8c363f62ffa99cf000a6b9c451"
 
 [[package]]
 name = "nom"
@@ -6204,7 +6204,6 @@ dependencies = [
  "unsigned-varint",
  "void",
  "wasm-timer",
- "yamux",
  "zeroize 1.1.0",
 ]
 
@@ -9127,9 +9126,9 @@ checksum = "d089681aa106a86fade1b0128fb5daf07d5867a509ab036d99988dec80429a57"
 
 [[package]]
 name = "yamux"
-version = "0.4.2"
+version = "0.4.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "902f4cee32c401c211b6b69f4a3f6f4cf3515644db5bd822cf685a7dbd6201f9"
+checksum = "d73295bc9d9acf89dd9336b3b5f5b57731ee72b587857dd4312721a0196b48e5"
 dependencies = [
  "bytes 0.5.4",
  "futures 0.3.4",