Remove tarball after installing it in demo

[xuesichao]

Issue #: Our release script didn't remove react sdk tarball after installing it when deploying the demo. So when raising version bump PR, the tarball is included in the commit.

Description of changes:

• Simply run rm -rf <path_to_tarball> after installing tarball.
• Add *.tgz to .gitignore.

Testing

1. Have you successfully run npm run build:release locally? N/A, just script change.

2. How did you test these changes? Test the release script and confirm the tarball is deleted.

3. If you made changes to the component library, have you provided corresponding documentation changes? N/A

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.