got rid of GoSub ast node and codegen complexity related to that.

sometimes programs get smaller, sometimes bigger.

codeGenVirtual/test/Dummies.kt

@@ -1,6 +1,9 @@
 package prog8tests.vm.helpers
 
-import prog8.code.core.*
+import prog8.code.core.DataType
+import prog8.code.core.Encoding
+import prog8.code.core.IMemSizer
+import prog8.code.core.IStringEncoding
 
 
 internal object DummyMemsizer : IMemSizer {

codeGenVirtual/test/TestVmPeepholeOpt.kt

@@ -1,6 +1,5 @@
 package prog8tests.vm
 
-import io.kotest.assertions.fail
 import io.kotest.core.spec.style.FunSpec
 import io.kotest.matchers.shouldBe
 import prog8.code.SymbolTable