Remove confusing Nil description

Part of #3760

Author: coke

doc/Language/nativecall.rakudoc

@@ -902,7 +902,7 @@ or C<CPointer>.
 
     sub explicitly-manage($str) is export(:DEFAULT)
 
-This returns a C<CStr> object for the given L<C<Str>|/type/Str>. If the string returned is
+This returns an object for the given L<C<Str>|/type/Str>. If the string returned is
 passed to a NativeCall subroutine, it will not be freed by the runtime's
 garbage collector.
 

doc/Type/Nil.rakudoc

@@ -2,7 +2,7 @@
 
 =TITLE class Nil
 
-=SUBTITLE Absence of a value or a benign failure
+=SUBTITLE Absence of a value
 
     class Nil is Cool { }