curl-config.in: eliminate double quotes around CURL_CA_BUNDLE

Otherwise it expands to:

    echo ""/etc/pki/tls/certs/ca-bundle.crt""

Detected by ShellCheck:

    curl-config:74:16: warning: The double quotes around this do
    nothing.  Remove or escape them. [SC2140]

curl-config.in

@@ -71,7 +71,7 @@ while test $# -gt 0; do
         ;;
 
     --ca)
-        echo "@CURL_CA_BUNDLE@"
+        echo @CURL_CA_BUNDLE@
         ;;
 
     --cc)