Remove the duplicated dead mac branch in Os.detect #938

Context

Os.detect(description: String) in core/src/commonMain/kotlin/it/unibo/tuprolog/Os.kt maps a free-form OS description (on the JVM, the os.name system property, see core/src/jvmMain/kotlin/it/unibo/tuprolog/Introspection.kt) to an Os value. Its when has the same mac branch twice:

description.contains("mac", ignoreCase = true) -> MAC
description.contains("mac", ignoreCase = true) -> MAC   // unreachable duplicate

The second branch can never match, because the first one already handles every input that contains mac. It does not change behavior, but it is dead code and looks like a copy-paste slip.

Expected

Each OS pattern appears once in Os.detect.

Possible approach

Delete the duplicate line. Optional: check whether another pattern was meant to go there (e.g. darwin or os x). Before adding darwin, note that the win branch is checked earlier and also matches "darwin". Today that cannot happen, because the only caller passes the JVM's os.name (Mac OS X on macOS).

Affected module: :core.

Original description

Os.detect contains a duplicated, dead mac match branch. Spotted during the documentation pass; not fixed in commit 5dfb787.