cleanup: removes uneeded annotation when not using network policy (#1884)

#### What type of PR is this?

<!--
Add one of the following kinds:
/kind bug
/kind documentation
/kind feature
-->

/kind cleanup

#### What this PR does / why we need it:

Removes the network policy annotation which is not needed (we are not
generating network policy)

#### Which issue(s) this PR fixes:
<!--
*Automatically closes linked issue when PR is merged.
Usage: `Fixes #<issue number>`, or `Fixes (paste link of issue)`.
-->
Fixes https://github.com/kubernetes/kompose/issues/1759

#### Special notes for your reviewer:

script/test/fixtures/statefulset/output-k8s.yaml

@@ -50,7 +50,6 @@ spec:
   template:
     metadata:
       labels:
-        io.kompose.network/statefulset-default: "true"
         io.kompose.service: db
     spec:
       containers:
@@ -100,7 +99,6 @@ spec:
   template:
     metadata:
       labels:
-        io.kompose.network/statefulset-default: "true"
         io.kompose.service: wordpress
     spec:
       containers:

script/test/fixtures/statefulset/output-os.yaml

@@ -46,7 +46,6 @@ spec:
   template:
     metadata:
       labels:
-        io.kompose.network/statefulset-default: "true"
         io.kompose.service: db
     spec:
       containers:
@@ -96,7 +95,6 @@ spec:
   template:
     metadata:
       labels:
-        io.kompose.network/statefulset-default: "true"
         io.kompose.service: db
     spec:
       containers:
@@ -166,7 +164,6 @@ spec:
   template:
     metadata:
       labels:
-        io.kompose.network/statefulset-default: "true"
         io.kompose.service: wordpress
     spec:
       containers:
@@ -216,7 +213,6 @@ spec:
   template:
     metadata:
       labels:
-        io.kompose.network/statefulset-default: "true"
         io.kompose.service: wordpress
     spec:
       containers: