Remove empty line after let in

According to https://github.com/NixOS/rfcs/blob/master/rfcs/0166-nix-formatting.md

packages/audiorelay.nix

@@ -45,7 +45,6 @@ let
     startupWMClass = "com-azefsw-audioconnect-desktop-app-MainKt";
   };
 in
-
 stdenv.mkDerivation {
   pname = "audiorelay";
   version = "0.27.5";

packages/compileOptimized/C.nix

@@ -17,7 +17,6 @@ let
 			++ lib.optional enableNativeOptimizations "-march=native"
 			++ additionalFlags;
 in
-
 pkg.overrideAttrs (prevAttrs: {
 	env.NIX_CFLAGS_COMPILE = (prevAttrs.env.NIX_CFLAGS_COMPILE or "")
 							 + lib.strings.concatStringsSep " " flags;

packages/compileOptimized/Rust.nix

@@ -45,7 +45,6 @@ let
   ++ lib.optional enableNoPIC "relocation-model=static"
   ++ lib.optional enableNativeOptimizations "target-cpu=native";
 in
-
 pkg.overrideAttrs (finalAttrs: prevAttrs: {
   cargoBuildType = "release";