Revert "Merge branch 'v3-alpha_linux' into v3-alpha"

This reverts commit b317efaf2c, reversing
changes made to 29b9c5200f.

v3/pkg/application/mainthread_linux.go

@@ -1,51 +0,0 @@
-//go:build linux
-
-package application
-
-/*
-#cgo linux pkg-config: gtk+-3.0
-
-#include <stdio.h>
-#include "gtk/gtk.h"
-
-typedef struct CallbackID
-{
-    unsigned int value;
-} CallbackID;
-
-extern void dispatchOnMainThreadCallback(unsigned int);
-
-static gboolean dispatchCallback(gpointer data) {
-    struct CallbackID *args = data;
-    unsigned int cid = args->value;
-    dispatchOnMainThreadCallback(cid);
-    free(args);
-
-    return G_SOURCE_REMOVE;
-};
-
-static void dispatchOnMainThread(unsigned int id) {
-    CallbackID *args = malloc(sizeof(CallbackID));
-    args->value = id;
-    g_idle_add((GSourceFunc)dispatchCallback, (gpointer)args);
-}
-
-*/
-import "C"
-
-func (m *linuxApp) dispatchOnMainThread(id uint) {
-	C.dispatchOnMainThread(C.uint(id))
-}
-
-//export dispatchOnMainThreadCallback
-func dispatchOnMainThreadCallback(callbackID C.uint) {
-	mainThreadFunctionStoreLock.RLock()
-	id := uint(callbackID)
-	fn := mainThreadFunctionStore[id]
-	if fn == nil {
-		Fatal("dispatchCallback called with invalid id: %v", id)
-	}
-	delete(mainThreadFunctionStore, id)
-	mainThreadFunctionStoreLock.RUnlock()
-	fn()
-}