Fix expecting content-type headers

It does not contain the charset anymore, for an unknown reason. It's not a
big deal though, so just fix it.

this should've been done with: I0583a8cedfecb9353d23978269f8a6f1fee171a4

Change-Id: Ic5ee2197d23d4bcf01a5faca2b470e8896d178d0

aodh/tests/functional/gabbi/gabbits-live/alarms.yaml

@@ -38,7 +38,7 @@ tests:
       status: 201
       response_headers:
           location: /$SCHEME://$NETLOC/v2/alarms/
-          content-type: application/json; charset=UTF-8
+          content-type: application/json
       response_json_paths:
           $.severity: low
           $.threshold_rule.threshold: 300.0
@@ -53,7 +53,7 @@ tests:
           $.threshold_rule.threshold: 300.0
           $.threshold_rule.comparison_operator: eq
       response_headers:
-          content-type: application/json; charset=UTF-8
+          content-type: application/json
 
     - name: updateAlarm
       desc: Updates a specified alarm.
@@ -101,7 +101,7 @@ tests:
       desc: Gets the state of a specified alarm.
       GET: /v2/alarms/$RESPONSE['$[0].alarm_id']/state
       response_headers:
-          content-type: application/json; charset=UTF-8
+          content-type: application/json
       response_json_paths:
           $: alarm