Remove unsupported dockerfiles and update docs

[leogr]

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

/kind feature

If contributing rules or changes to rules, please make sure to also uncomment one of the following line:

/kind rule-update

/kind rule-create

Any specific area of the project related to this PR?

Uncomment one (or more) /area <> lines:

/area build

/area engine

/area examples

/area rules

/area integrations

/area tests

/area proposals

What this PR does / why we need it:

This PR clean ups unsupported dockerfiles and update the related README as discussed here.

Which issue(s) this PR fixes:

Fixes #1019

Special notes for your reviewer:
Note that I have not renamed the event generator, because of #1089 is still in progress.

Does this PR introduce a user-facing change?:

update(docker): remove RHEL, kernel/linuxkit, and kernel/probeloader images

[leodido]

Finally!

Thanks for bringing my markdown table here, too 😆

[poiana]

LGTM label has been added.

Git tree hash: bde450b2deeecc054246d271748bbb4a3f0d8885

[fntlnz]

I like this! Thanks a lot @leogr

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fntlnz, leodido

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