Remove dead objc setup code

[keith]

This appears to be unused

[keith]

@trybka continuing from #12046 (comment)

if no one references LIBTOOL_ATTRIBUTE does that mean this is unreferenced entirely? I assumed that the registration of the LibtoolRule might mean it could be used implicitly somehow?

[trybka]

Good find on LibtoolRule. My read of this is that any caller which would want to invoke this libtool would need to grab it via the attribute (or calling the getter), and since I can't find those references, I think the whole mess is unused? Curious how far on the thread this can be pulled out.

[keith]

I will push a second commit with that assumption after I validate I can build our app without that attribute

[keith]

if all it was doing was adding that implicit attribute, I would assume that someone would have to reference $libtool (even if not with the constant) to use it? similar to

bazel/src/main/java/com/google/devtools/build/lib/analysis/test/TestActionBuilder.java

Lines 245 to 246 in 24a082d

	} else if (ruleContext.isAttrDefined("$lcov_merger", LABEL)) {
	lcovMergerAttr = "$lcov_merger";

or

bazel/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java

Line 1452 in 24a082d

Artifact pruner = ruleContext.getPrerequisiteArtifact("$j2objc_dead_code_pruner");

[trybka]

if all it was doing was adding that implicit attribute, I would assume that someone would have to reference $libtool (even if not with the constant) to use it?

That's my understanding, yes.

[trybka]

+cc @googlewalt as an FYI

[keith]

hrm based on the code in rules_apple, this might work inside google? https://github.com/bazelbuild/rules_apple/blob/0a1cbce9b3d169269313aba1113d2aa0a8c3c514/apple/internal/testing/apple_test_rule_support.bzl#L124-L128

[trybka]

Let's put the apple_sdk flag back for now, there are more references to it internally, and we'd need to clean them up.

You can probably still remove the getters and whatnot

[keith]

added that flag back

[keith]

Thanks a ton!~