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)`.
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Fixes https://github.com/kubernetes/kompose/issues/1759

#### Special notes for your reviewer:

script/test/fixtures/env-multiple/output-k8s.yaml

@@ -56,7 +56,6 @@ spec:
     metadata:
       creationTimestamp: null
       labels:
-        io.kompose.network/env-default: "true"
         io.kompose.service: another-namenode
     spec:
       containers:
@@ -117,7 +116,6 @@ spec:
     metadata:
       creationTimestamp: null
       labels:
-        io.kompose.network/env-default: "true"
         io.kompose.service: namenode
     spec:
       containers:

script/test/fixtures/env-multiple/output-os.yaml

@@ -78,7 +78,6 @@ spec:
     metadata:
       creationTimestamp: null
       labels:
-        io.kompose.network/env-default: "true"
         io.kompose.service: another-namenode
     spec:
       containers:
@@ -151,7 +150,6 @@ spec:
     metadata:
       creationTimestamp: null
       labels:
-        io.kompose.network/env-default: "true"
         io.kompose.service: namenode
     spec:
       containers: