Update to 1.20.4

buildSrc/src/main/kotlin/cc-tweaked.java-convention.gradle.kts

@@ -40,21 +40,10 @@ repositories {
 
     val mainMaven = maven("https://squiddev.cc/maven") {
         name = "SquidDev"
-        content {
-            // Until https://github.com/SpongePowered/Mixin/pull/593 is merged
-            includeModule("org.spongepowered", "mixin")
-        }
     }
 
     exclusiveContent {
         forRepositories(mainMaven)
-
-        // Include the ForgeGradle repository if present. This requires that ForgeGradle is already present, which we
-        // enforce in our Forge overlay.
-        val fg =
-            project.extensions.findByType(net.minecraftforge.gradle.userdev.DependencyManagementExtension::class.java)
-        if (fg != null) forRepositories(fg.repository)
-
         filter {
             includeGroup("cc.tweaked")
             // Things we mirror