syscall: refer to Proc.Call documentation for LazyProc.Call on Windows

The documentation comment was duplicated for each of these methods, and
the LazyProc.Call documentation incorrectly mentioned that Call accepts
only 15 arguments, but it actually accepts 18 now.

To prevent further documentation drift, refer the reader to the
documentation for Proc.Call instead of duplicating it for LazyProc.Call.

In addition, note that LazyProc's Addr, Call, and Find methods each
trigger a procedure lookup.

Change-Id: I6756cf7601fba79d1414ff5a5d6eef900aa590e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/181199


Run-TryBot: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>