Currently we depend on libcurl for URL fetching in AWS extension common utils

The use of curl is largely redundant, since Envoy itself can do HTTP fetch. In addition, Curl does not have a compatible threading and observability model with Envoy. The recent disclosures of CVE-2020-8169 and CVE-2020-8177 provide an example of why we should eliminate this from our trusted compute base.

Opening this tracking ticket to discuss further whether we can remove this dep.