[Cleanup] Remove legacy `skip` tags from YAML tests

[msfroh]

Is your feature request related to a problem? Please describe

We sometimes need to skip YAML REST tests when running on old versions of OpenSearch, especially for the backward-compatibility (BWC) tests and mixed-cluster tests.

Mostly, this is for stuff that was not supported on old versions, where a mixed cluster would have nodes running a newer version that support the feature being tested, along with nodes from an earlier version that do not. Some of these skip entries are for predecessor versions, though, which we won't test in a mixed-cluster environment.

Describe the solution you'd like

It would be a nice cleanup to go through and remove the - skip: annotations from YAML REST tests where they refer to predecessor versions.

Here is a search that matches skips for 7.x versions in YAML tests (112 files right now): https://github.com/search?q=repo%3Aopensearch-project%2FOpenSearch+version%3A+%22+-+7%22+language%3AYAML&type=code

Here is a search for skips against 6.x versions (49 files, most checking version - 6.99.99 as a way of checking for 7.0+): https://github.com/search?q=repo%3Aopensearch-project%2FOpenSearch+version%3A+%22+-+6%22+language%3AYAML&type=code

I would suggest addressing these in two separate PRs. Removing the 6.x skips can be backported to the 2.x branch. I don't know if we can remove 7.x checks from the 2.x branch -- it looks like the code assumes 2.x is backward compatible with 7.10:

OpenSearch/libs/core/src/main/java/org/opensearch/Version.java

Lines 342 to 347 in 9498793

	protected Version computeMinCompatVersion() {
	if (major == 1 || major == 7) {
	// we don't have LegacyESVersion.V_6 constants, so set it to its last minor
	return LegacyESVersion.fromId(6080099);
	} else if (major == 2) {
	return LegacyESVersion.fromId(7100099);

Related component

Other

Describe alternatives you've considered

These skips aren't really hurting anyone. We could just leave them in place.

Eventually, though, if/when we release OpenSearch 5.0 and switch the main branch to 6.0, they might cause us to skip tests that we don't want to skip.

Additional context

No response

[rgsriram]

I like to contribute. Please assign it to me.