tool_operate: Don't use Windows CA store as a fallback

tool_operate: Don't use Windows CA store as a fallback

Background:

148534d added CURLSSLOPT_NATIVE_CA to use the Windows OS certificate
store in libcurl w/ OpenSSL on Windows. CURLSSLOPT_NATIVE_CA overrides
CURLOPT_CAINFO if both are set. The curl tool will fall back to
CURLSSLOPT_NATIVE_CA if it could not find a certificate bundle to set
via CURLOPT_CAINFO.

Problem:

libcurl may be built with hardcoded paths to a certificate bundle or
directory, and if CURLSSLOPT_NATIVE_CA is used then those paths are
ignored.

Solution:

A solution is still being discussed but since there's an impending
release this commit removes using CURLSSLOPT_NATIVE_CA in the curl tool.

Ref: https://github.com/curl/curl/issues/5585