Remove some unused dependencies

Author: djc

tokio-imap/Cargo.toml

@@ -20,9 +20,7 @@ maintenance = { status = "passively-maintained" }
 bytes = "0.4"
 futures = { version = "0.3.0-alpha.19", package = "futures-preview" }
 imap-proto = { version = "0.9.1", path = "../imap-proto" }
-native-tls = "0.2"
 nom = "5"
-rustls = "0.16.0"
 tokio = "0.2.0-alpha.6"
 tokio-rustls = "0.12.0-alpha.4"
 webpki-roots = "0.18.0"