Removes a given easy_handle from the multi_handle. This will make
the specified easy handle be removed from this multi handles control.
When the easy handle has been removed from a multi stack, it is again
perfectly legal to invoke curl_easy_perform(3) on this easy handle.
Removing an easy handle while being used is perfectly legal and will
effectively halt the transfer in progress involving that easy handle. All
other easy handles and transfers will remain unaffected.