Remove a useless debug message in filetransfer.cc

Remove the `verify TLS: Nix CA file = 'blah'` message that Nix used to print when fetching anything as it's both useless (`libcurl` prints the same info in its logs) and misleading (gives the impression that a new TLS connection is being established which might not be the case because of multiplexing. See #7011 )

src/libstore/filetransfer.cc

@@ -322,7 +322,6 @@ struct curlFileTransfer : public FileTransfer
             }
 
             if (request.verifyTLS) {
-                debug("verify TLS: Nix CA file = '%s'", settings.caFile);
                 if (settings.caFile != "")
                     curl_easy_setopt(req, CURLOPT_CAINFO, settings.caFile.c_str());
             } else {