Use rustls rather than native-tls in all dependencies.

We depends on rustls in postgres_backend anyway, so might as well use it
for all TLS stuff. Seems better to depend on only one library both from a
security point of view, and because fewer dependencies means less code to
compile. With this commit, we no longer depend on OpenSSL.

control_plane/Cargo.toml

@@ -17,7 +17,7 @@ anyhow = "1.0"
 thiserror = "1"
 nix = "0.23"
 url = "2.2.2"
-reqwest = { version = "0.11", features = ["blocking", "json"] }
+reqwest = { version = "0.11", default-features = false, features = ["blocking", "json", "rustls-tls"] }
 
 pageserver = { path = "../pageserver" }
 zenith_utils = { path = "../zenith_utils" }