LibGUI: Remove use of copy_ref().

Libraries/LibGUI/GDirectoryModel.cpp

@@ -149,7 +149,7 @@ GIcon GDirectoryModel::icon_for(const Entry& entry) const
             LOCKER(thumbnail_cache().lock());
             auto it = thumbnail_cache().resource().find(path);
             if (it != thumbnail_cache().resource().end()) {
-                entry.thumbnail = (*it).value.copy_ref();
+                entry.thumbnail = (*it).value;
             } else {
                 thumbnail_cache().resource().set(path, nullptr);
             }

Libraries/LibGUI/GIcon.cpp

@@ -11,7 +11,7 @@ GIcon::GIcon(const GIconImpl& impl)
 }
 
 GIcon::GIcon(const GIcon& other)
-    : m_impl(other.m_impl.copy_ref())
+    : m_impl(other.m_impl)
 {
 }
 

Libraries/LibGUI/GIcon.h

@@ -29,7 +29,8 @@ public:
 
     GIcon& operator=(const GIcon& other)
     {
-        m_impl = other.m_impl.copy_ref();
+        if (this != &other)
+            m_impl = other.m_impl;
         return *this;
     }