This hack was added in an attempt to continue supporting the experimental
(non-buildkit) `--platform` option, by dynamically updating the API version
required if buildkit isn't enabled.
This hack didn't work, however, because at the moment the override is
added, the command is not yet attached to the "root" (`docker`) command,
and because of that, the command itself is the `root` command;
`cmd.Root()` returned the `build` command.
As a result, validation steps defined as `PersistentPreRunE` on the root
command were not executed, causing invalid flags/options to not producing
an error.
Attempts to use an alternative approach (for example, cobra supports both
a `PersistentPreRun` and `PersistentPreRunE`) did not work either, because
`PersistentPreRunE` takes precedence over `PersistentPreRun`, and only one
will be executed.
Now that `--platform` should be supported for other cases than just for
experimental (LCOW), let's remove the 'experimental' check, and just assume
it's supported for API v1.32 and up.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>