Remove version matrix from README

[cartermckinnon]

What type of PR is this?

What this PR does / why we need it:

This gets rid of the version table from the README. We don't want to update this every time a release is cut on any of the active branches, and the compatibility is already clearly explained in the text.

https://github.com/kubernetes/cloud-provider-aws/issues/799#issuecomment-1869759028

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

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[cartermckinnon]

/assign @hakman

[dims]

/approve /lgtm

[k8s-ci-robot]

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