[Enhancement/Cleanup] Remove unused argument from `cmdSlot` function in osscluster

[kapurm17]

Description The cmdSlot function in the osscluster.go file accepts two parameters :

1. context
2. Cmder

The context argument is not being used in the the function and should be safe to remove.

Code Snippet:

func (c *ClusterClient) cmdSlot(ctx context.Context, cmd Cmder) int {
    args := cmd.Args()
    if args[0] == "cluster" && args[1] == "getkeysinslot" {
        return args[2].(int)
    }

    return cmdSlot(cmd, cmdFirstKeyPos(cmd))
}

CodeRef: https://github.com/redis/go-redis/blob/master/osscluster.go#L1814

What I expect to see?

• Remove context from the cmdSlot function definition and all the instances where we are calling this from.

What version of go-redis are you using? checked the same on the master branch

[kapurm17]

@chayim @ofekshenawa I can start on the PR, if the change looks good?