[vm/ffi] Update DynamicLibrary.process() documentation

https://dart-review.googlesource.com/c/sdk/+/260760 added support for
Windows to `DynamicLibrary.process()` but forgot to update the dartdoc
comment.

Change-Id: Ic8533e4d1bb23009753bcdef446e2cfe49dea0f6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/264940
Commit-Queue: Daco Harkes <[email protected]>
Auto-Submit: Daco Harkes <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Martin Kustermann <[email protected]>

Author: dcharkes

sdk/lib/ffi/dynamic_library.dart

@@ -13,8 +13,6 @@ class DynamicLibrary {
   ///
   /// Any symbol in a library currently loaded with global visibility
   /// (including the executable itself) may be resolved through this library.
-  ///
-  /// This feature is not available on Windows.
   external factory DynamicLibrary.process();
 
   /// Creates a [DynamicLibrary] containing all the symbols of the running