refactor(paroxysm): Explicitly macro imports, no more 'extern crate'

Removes all but one occurence of `extern crate`, to conform with Rust
2018.

The last one is necessary because Diesel is a giant jungle of
complicated macros re-exported from private crates, and the current
version makes it hard to import those directly instead.

Change-Id: Id14165a456d5c3ce6f7a4e0222c611640113eb11
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1549
Tested-by: BuildkiteCI
Reviewed-by: kanepyork <rikingcoding@gmail.com>

fun/paroxysm/default.nix

@@ -7,5 +7,10 @@ pkgs.naersk.buildPackage {
   name = "paroxysm";
   version = "0.0.1";
   src = ./.;
-  buildInputs = [pkgs.openssl pkgs.pkgconfig pkgs.postgresql.lib];
+
+  buildInputs = with pkgs; [
+    openssl
+    pkgconfig
+    postgresql.lib
+  ];
 }