Remove docs note about fused types being "experimental". They are old enough...

Remove docs note about fused types being "experimental". They are old enough by now to consider them an established language feature.

docs/src/userguide/fusedtypes.rst

@@ -14,8 +14,6 @@ Java / C#.
 
 .. _generic programming: https://en.wikipedia.org/wiki/Generic_programming
 
-.. Note:: Support is still somewhat experimental, there may be bugs!
-
 .. Note:: Fused types are not currently supported as attributes of extension
           types.  Only variables and function/method arguments can be declared
           with fused types.