docs: Support gRPC without TLS

[SpringMT]

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking
/kind bug
/kind cleanup

/kind documentation

/kind feature
/kind hotfix

What this PR does / Why we need it:
In this PR #2272, support gRPC without TLS.
So, remove the text that Only applicable to the REST API. It currently does not work for the gRPC API..

Which issue(s) this PR fixes:

Closes #

Special notes for your reviewer:

[agones-bot]

Build Failed 😱

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[markmandel]

Thanks for the fix - we're in the process of getting the RC in, so will swing back around once that is complete.

[agones-bot]

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• image: gcr.io/agones-images/agones-controller:1.21.0-78f157d
• image: gcr.io/agones-images/agones-ping:1.21.0-78f157d
• Linux C++ SDK (build): agonessdk-1.21.0-78f157d-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.21.0-78f157d.zip

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To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2472/head:pr_2472 && git checkout pr_2472
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.21.0-78f157d

[agones-bot]

Build Succeeded 👏

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The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.21.0-d6a915e
• image: gcr.io/agones-images/agones-ping:1.21.0-d6a915e
• Linux C++ SDK (build): agonessdk-1.21.0-d6a915e-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.21.0-d6a915e.zip

A preview of the website (the last 30 builds are retained):

• https://d6a915e-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2472/head:pr_2472 && git checkout pr_2472
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.21.0-d6a915e

[agones-bot]

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The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.22.0-bdd8154
• image: gcr.io/agones-images/agones-ping:1.22.0-bdd8154
• Linux C++ SDK (build): agonessdk-1.22.0-bdd8154-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.22.0-bdd8154.zip

A preview of the website (the last 30 builds are retained):

• https://bdd8154-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2472/head:pr_2472 && git checkout pr_2472
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.22.0-bdd8154

[agones-bot]

Build Succeeded 👏

Build Id: 4894ea8b-24b2-44b6-9ba1-2f2888e77db3

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.22.0-98ab3d7
• image: gcr.io/agones-images/agones-ping:1.22.0-98ab3d7
• Linux C++ SDK (build): agonessdk-1.22.0-98ab3d7-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.22.0-98ab3d7.zip

A preview of the website (the last 30 builds are retained):

• https://98ab3d7-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2472/head:pr_2472 && git checkout pr_2472
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.22.0-98ab3d7

[agones-bot]

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Build Id: 8e4267a0-6ece-4f79-b465-73120c0c892b

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.22.0-d414c74
• image: gcr.io/agones-images/agones-ping:1.22.0-d414c74
• Linux C++ SDK (build): agonessdk-1.22.0-d414c74-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.22.0-d414c74.zip

A preview of the website (the last 30 builds are retained):

• https://d414c74-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2472/head:pr_2472 && git checkout pr_2472
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.22.0-d414c74

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: roberthbailey, SpringMT

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