refactor: Removed Promise Polyfill to reduce bundle size

[zashraf1985]

Summary

Removed Promise Polyfill from browser entry point to reduce bundle size. A user can still use the SDK in older browsers by including the promise polyfill themselves.

Test plan

All tests pass by providing promise polyfill as part of the test setup.

[coveralls]

Coverage decreased (-0.0003%) to 97.222% when pulling 4ad521b on zeeshan/remove-promise-polyfill into 5cf5ddc on master.

[mikeproeng37]

I think we need to remove the promise-polyfill library from our dependencies or at least move it to dev-dependencies since we use it for testing: https://github.com/optimizely/javascript-sdk/blob/master/packages/optimizely-sdk/package.json#L43

[zashraf1985]

I think we need to remove the promise-polyfill library from our dependencies or at least move it to dev-dependencies since we use it for testing: https://github.com/optimizely/javascript-sdk/blob/master/packages/optimizely-sdk/package.json#L43

Yes you are right. This should have been moved to dev dependencies. This is done now.

[mikeproeng37]

lgtm