fix: drop deprecated macosX64 target, keep only macosArm64

macosX64 (Intel) has been removed from Kotlin's native target tiers.
Only macosArm64 (Apple Silicon) is supported.

https://claude.ai/code/session_01WSNE6QKiYM2ZutQD2UihCW

quartz/build.gradle.kts

@@ -87,7 +87,6 @@ kotlin {
 
     linuxX64()
 
-    macosX64()
     macosArm64()
 
     // This makes sure that the resource file directory is visible for iOS tests.
@@ -310,14 +309,6 @@ kotlin {
                 dependsOn(appleTest)
             }
 
-        val macosX64Main by getting {
-            dependsOn(macosMain)
-        }
-
-        val macosX64Test by getting {
-            dependsOn(macosTest)
-        }
-
         val macosArm64Main by getting {
             dependsOn(macosMain)
         }