influxdb2-server: use structuredAttrs instead of passAsFile

pkgs/by-name/in/influxdb2-server/package.nix

@@ -62,16 +62,18 @@ let
       Cflags: -I/out/include
       Libs: -L/out/lib -lflux -lpthread
     '';
-    passAsFile = [ "pkgcfg" ];
     postInstall = ''
       mkdir -p $out/include $out/pkgconfig
       cp -r $NIX_BUILD_TOP/${finalAttrs.src.name}/libflux/include/influxdata $out/include
-      substitute $pkgcfgPath $out/pkgconfig/flux.pc \
+      printf "%s" "$pkgcfg" > $out/pkgconfig/flux.pc
+      substituteInPlace $out/pkgconfig/flux.pc \
         --replace-fail /out $out
     ''
     + lib.optionalString stdenv.hostPlatform.isDarwin ''
       install_name_tool -id $out/lib/libflux.dylib $out/lib/libflux.dylib
     '';
+
+    __structuredAttrs = true;
   });
 in
 buildGoModule {