Remove available branching for macOS <12

[jathu]

We recently bumped the minimum target macOS version to 12.0. So, comb through the code and remove branching where the macOS version is below 12.0.

Search for @available:

grep "@available"

Example of a candidate where we branch on a macOS min version of 11.0:

executorch/backends/apple/coreml/runtime/delegate/ETCoreMLModelManager.mm

Lines 95 to 107 in 3f91780

	if (@available(macOS 11.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *)) {
	NSMutableDictionary<NSString *, id> *output_backings = [NSMutableDictionary dictionary];
	NSEnumerator<NSString *> *enumerator = [output_names objectEnumerator];
	for (MLMultiArray *output in outputs) {
	NSString *output_name = [enumerator nextObject];
	if (output_name.length == 0) {
	ETCoreMLLogErrorAndSetNSError(error, ETCoreMLErrorCorruptedModel, "Model is broken.");
	return nil;
	}
	output_backings[output_name] = output;
	}
	options.outputBackings = output_backings;
	}

[NeelakshSharma]

Hi @jathu , can i work on this issue?

[NeelakshSharma]

Also do i just remove the macOS 11.0 branching or am also supposed to replace with macOS 12.0 ?

[jathu]

@NeelakshSharma yup, feel free to submit a PR!

Also do i just remove the macOS 11.0 branching or am also supposed to replace with macOS 12.0 ?

You should be able to just remove the check since we've bumped the min version in the compiler. You can learn more about it here: https://developer.apple.com/documentation/swift/marking-api-availability-in-objective-c

[NeelakshSharma]

Hi @jathu , I have incorporated your comments and raised a PR. This is the first time I'm contributing for open source. Refer PR link