MAINT-7081: Eliminate unused variable errors after new refactoring.

The new helper functions check_curl_easy_setopt() and
check_curl_multi_setopt() encapsulate the pervasive idiom:

    code = curl_{easy,multi}_setopt(handle, option, arg);
    check_curl_{easy,multi}_code(code, option);

But since each of these helper functions contains its own local CURL{,M}code
variable 'code', having a caller-scope variable reused for every such call is
no longer necessary -- in fact is no longer used at all. That produces a fatal
warning with MSVC. Get rid of those now-unused variables.

indra/llcorehttp/_httplibcurl.cpp

@@ -470,7 +470,6 @@ void HttpLibcurl::policyUpdated(int policy_class)
 		
 		HttpPolicyClass & options(policy.getClassOptions(policy_class));
 		CURLM * multi_handle(mMultiHandles[policy_class]);
-		CURLMcode code;
 
 		// Enable policy if stalled
 		policy.stallPolicy(policy_class, false);

indra/llcorehttp/_httpoprequest.cpp

@@ -460,8 +460,6 @@ void HttpOpRequest::setupCommon(HttpRequest::policy_t policy_id,
 // *TODO:  Move this to _httplibcurl where it belongs.
 HttpStatus HttpOpRequest::prepareRequest(HttpService * service)
 {
-	CURLcode code;
-	
 	// Scrub transport and result data for retried op case
 	mCurlActive = false;
 	mCurlHandle = NULL;