olivetin: improve reproducibility of gen derivation (#439358)

pkgs/by-name/ol/olivetin/package.nix

···
         runHook postInstall
       '';
 
+      postFixup = ''
+        find $out -type f -name '*.go' -exec \
+          sed -i -E 's|//.*protoc-gen-go(-grpc)? +v.*$||' {} +
+      '';
+
       outputHashMode = "recursive";
-      outputHash = "sha256-o+Zt3rmTK7NmBQ9hDlbxZySUlCx6Ks7yQTtdm9+pJac=";
+      outputHash = "sha256-wHqXsSV18mF/CfLQ0S4rGtT3QRcLnneYXAa8nXZaHpQ=";
     };
 
     webui = buildNpmPackage {