Remove obsolote statement about msg.sender and library calls.

docs/units-and-global-variables.rst

@@ -84,11 +84,6 @@ Block and Transaction Properties
     but the only guarantee is that it will be somewhere between the timestamps of two
     consecutive blocks in the canonical chain.
 
-.. note::
-    If you want to implement access restrictions in library functions using
-    ``msg.sender``, you have to manually supply the value of
-    ``msg.sender`` as an argument.
-
 .. note::
     The block hashes are not available for all blocks for scalability reasons.
     You can only access the hashes of the most recent 256 blocks, all other