feat: update Localytics to v4 and remove root event forwarder

[mmustafa-tse]

Summary

• Localytics have released a major version v4 to their Web SDK as mentioned here while our current kit still uses v3. Also, I removed the LocalyticsEventForwarder.js file from the root of this repo as we have transitioned to using forwarders files in src folders

Testing Plan

• Was this tested locally? If not, explain why.
• E2E and unit tested

Reference Issue (For mParticle employees only. Ignore if you are an outside contributor)

• Closes https://go.mparticle.com/work/SQDSDKS-6429