Remove method parameter for composable version checks

[thecoop]

This parameter is only null, so I think it can probably go...

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[dakrone]

@droberts195 I think you added this parameter, going from the Git blame. Do you have any reason it couldn't be removed?

[droberts195]

I added the parameter in #73232 to aid the switchover of ML and transform templates from legacy templates to composable templates. During the switchover period it was possible that we'd need to install a newer legacy template rather than switching to a composable template while the cluster was in a mixed-version state where the older versions didn't understand composable templates. That situation can never happen now because any version from 7.17 upwards must understand composable templates.

It's OK to get rid of the argument. It's interesting that the SAML template is still a legacy template. The changes in this PR are making the checkTemplateExistsAndIsUpToDate method specific to legacy templates now, so might make any subsequent shift to composable templates for security harder. But if you're happy to defer that work to later then this change won't cause any problems.

[dakrone]

LGTM