Avoid enforcing XCode version is shared code.

shared/src/main/kotlin/org/jetbrains/kotlin/konan/target/KonanProperties.kt

@@ -68,8 +68,6 @@ fun Properties.keepOnlyDefaultProfiles() {
 
     // Force build to use only 'default' profile:
     this.setProperty(DEPENDENCY_PROFILES_KEY, "default")
-    // Force build to use fixed Xcode version:
-    this.setProperty("useFixedXcodeVersion", "10.1")
     // TODO: it actually affects only resolution made in :dependencies,
     // that's why we assume that 'default' profile comes first (and check this above).
 }