chore: remove unused angular deps

[KenLSM]

Problem

A continuation of #6344.
We are currently still having several dependencies that were used previously by angular. These dependencies would 1) slow down our build (and by extension deployment), as well as dependabot raising distractive PRs to bump these unused dependencies.

Solution

Breaking Changes

• No - this PR is backwards compatible

Tests

React bundling should be unaffected

• can view FormSG React homepage

Deploy Notes

Removed dev dependencies:

• copy-webpack-plugin : used in angular to copy static assets for the file server to serve
• google-fonts-plugin : used in angular only
• mini-css-extract-plugin : used in angular's webpack to chunk css, from our angular code, by page
• optimize-css-assets-webpack-plugin : used in angular's webpack to run various css optimization
• terser-webpack-plugin : used in angular's webpack to
• webpack-merge : used in angular's webpack

[KenLSM]

Should also naturally make PR #6371, and #6371 from dependabot irrelevant.