hacky lambda process.env fix"

fix linting issues

update changelog

fix polyfill check

use AWS_EXECUTION_ENV

fix styling

fix version check

Update CHANGELOG.md

…motives.

The work in #2054 was
designed in a way that, irregardless of the environment, the
`graphql-upload` package would only be loaded if uploads were enabled.
Therefore, the guard which checks `process.env.AWS_EXECUTION_ENV` should no
longer be necessary.

Additionally, we don't need to prefix our type-only variables with
underscores, as that's not a style that we've otherwise adopted.