introduce tfHasOwned for fast must-move checkings; removed tfAcyclic as the GC has ignored this hint for quite some time now

doc/manual.rst

@@ -6925,41 +6925,8 @@ The ``noreturn`` pragma is used to mark a proc that never returns.
 
 acyclic pragma
 --------------
-The ``acyclic`` pragma can be used for object types to mark them as acyclic
-even though they seem to be cyclic. This is an **optimization** for the garbage
-collector to not consider objects of this type as part of a cycle:
-
-.. code-block:: nim
-  type
-    Node = ref NodeObj
-    NodeObj {.acyclic.} = object
-      left, right: Node
-      data: string
-
-Or if we directly use a ref object:
-
-.. code-block:: nim
-  type
-    Node = ref object {.acyclic.}
-      left, right: Node
-      data: string
-
-In the example a tree structure is declared with the ``Node`` type. Note that
-the type definition is recursive and the GC has to assume that objects of
-this type may form a cyclic graph. The ``acyclic`` pragma passes the
-information that this cannot happen to the GC. If the programmer uses the
-``acyclic`` pragma for data types that are in reality cyclic, the GC may leak
-memory, but nothing worse happens.
-
-**Future directions**: The ``acyclic`` pragma may become a property of a
-``ref`` type:
-
-.. code-block:: nim
-  type
-    Node = acyclic ref NodeObj
-    NodeObj = object
-      left, right: Node
-      data: string
+The ``acyclic`` pragma applies to type declarations. It is deprecated and
+ignored.
 
 
 final pragma