transform: remove switched func lowering

The switched func lowering was mainly necessary for coroutines.
With coroutines removed, this is no longer necessary.

compiler/testdata/func.ll

@@ -0,0 +1,47 @@
+; ModuleID = 'func.go'
+source_filename = "func.go"
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128-ni:1:10:20"
+target triple = "wasm32-unknown-wasi"
+
+declare noalias nonnull i8* @runtime.alloc(i32, i8*, i8*, i8*)
+
+declare void @runtime.trackPointer(i8* nocapture readonly, i8*, i8*)
+
+; Function Attrs: nounwind
+define hidden void @main.init(i8* %context, i8* %parentHandle) unnamed_addr #0 {
+entry:
+  ret void
+}
+
+; Function Attrs: nounwind
+define hidden void @main.foo(i8* %callback.context, void ()* %callback.funcptr, i8* %context, i8* %parentHandle) unnamed_addr #0 {
+entry:
+  %0 = icmp eq void ()* %callback.funcptr, null
+  br i1 %0, label %fpcall.throw, label %fpcall.next
+
+fpcall.throw:                                     ; preds = %entry
+  call void @runtime.nilPanic(i8* undef, i8* null) #0
+  unreachable
+
+fpcall.next:                                      ; preds = %entry
+  %1 = bitcast void ()* %callback.funcptr to void (i32, i8*, i8*)*
+  call void %1(i32 3, i8* %callback.context, i8* undef) #0
+  ret void
+}
+
+declare void @runtime.nilPanic(i8*, i8*)
+
+; Function Attrs: nounwind
+define hidden void @main.bar(i8* %context, i8* %parentHandle) unnamed_addr #0 {
+entry:
+  call void @main.foo(i8* undef, void ()* bitcast (void (i32, i8*, i8*)* @main.someFunc to void ()*), i8* undef, i8* undef)
+  ret void
+}
+
+; Function Attrs: nounwind
+define hidden void @main.someFunc(i32 %arg0, i8* %context, i8* %parentHandle) unnamed_addr #0 {
+entry:
+  ret void
+}
+
+attributes #0 = { nounwind }