chore(exllama): drop exllama backend (#3536)

* chore(exllama): drop exllama backend

For polishing and cleaning up it makes now sense to drop exllama which
is completely unmaintained, and was only supporting the llamav1
architecture (nowadays it's superseded by llamav1) .

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* chore(gosec): fix CI

downgrade to latest known version of the gosec action

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

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Signed-off-by: Ettore Di Giacinto <mudler@localai.io>