shellcheck: fix several occurences of SC2034

message:
SC2034: $VARNAME appears unused. Verify it or export it.

most of these are related to the style:
we generate global vars, which are used in other functions.

the var "lexical_url" was really unused (left it as comment)

the travis-check now does not need anymore special flags.

Signed-off-by: Bastian Bittorf <bb@npl.de>

dnsapi/dns_gd.sh

@@ -98,8 +98,8 @@ _gd_rest() {
   data="$3"
   _debug "$ep"
 
-  _H1="Authorization: sso-key $GD_Key:$GD_Secret"
-  _H2="Content-Type: application/json"
+  export _H1="Authorization: sso-key $GD_Key:$GD_Secret"
+  export _H2="Content-Type: application/json"
 
   if [ "$data" ]; then
     _debug data "$data"