chore: remove a stray .js file

When we moved a `.js` file to a `.ts` file in
#36272, forgot to ignore the `.js`
file.

Do that now.

Author: rix0rrr

packages/@aws-cdk/custom-resource-handlers/.gitignore

@@ -32,4 +32,3 @@ scripts/*.d.ts
 
 !lib/aws-certificatemanager/dns-validated-certificate-handler/index.js
 !test/aws-certificatemanager/dns-validated-certificate-handler.test.js
-!lib/aws-cloudfront/edge-function/index.js