fix: cleanup custom functions docs

removed duplicated lines

Author: pavinthan

src/pages/[platform]/build-a-backend/functions/custom-functions/index.mdx

@@ -113,9 +113,7 @@ import { fileURLToPath } from "node:url";
 import { defineFunction } from "@aws-amplify/backend";
 import { DockerImage, Duration } from "aws-cdk-lib";
 import { Code, Function, Runtime } from "aws-cdk-lib/aws-lambda";
-import { defineFunction } from "@aws-amplify/backend";
-import { DockerImage, Duration } from "aws-cdk-lib";
-import { Code, Function, Runtime } from "aws-cdk-lib/aws-lambda";
+
 export const sayHelloFunctionHandler = defineFunction(
   (scope) =>
     new Function(scope, "say-hello", {