chore: remove duplicate default-allow-same-namespace network policy

[akagami-harsh]

Description of your changes:

This PR removes allow-same-namespace-networkpolicy.yaml, because it creates duplication in manifests repo and should only exist in KFP test manifests

• related comment
  Synchronize kubeflow pipelines manifests 2.15.0 manifests#3283 (comment)

[google-oss-prow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[akagami-harsh]

cc @juliusvonkohout

[hbelmiro]

/lgtm

[juliusvonkohout]

Thank you, otherwise I have KFP 2.5.1 already successfully in kubeflow platform / manifests. It is a great release. It did clash with https://github.com/kubeflow/manifests/blob/master/common/networkpolicies/base/default-allow-same-namespace.yaml
CC @droctothorpe @akagami-harsh for approval.

[droctothorpe]

/lgtm
/approve

[google-oss-prow]

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