Revert "Enable cursor compositing for uncurtained Mac."

This change breaks non-curtained multimon since you can no longer
switch between monitors. 

This reverts commit d8b19b69.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Enable cursor compositing for uncurtained Mac.
> 
> I previously thought that the cursor was always part of the captured
> screen on Mac, but it turns out that's only true if curtain mode is
> active. This CL makes creating of a composing capturer conditional
> on the curtain mode setting, which should give the correct beheviour
> for both remote support and uncurtained remote access.
> 
> Bug: 1048774
> Change-Id: I28cc01b0b615794e06cd31308c10a40af550e0e1
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2036546
> Commit-Queue: Jamie Walch <jamiewalch@chromium.org>
> Reviewed-by: Joe Downing <joedow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#738347}

TBR=jamiewalch@chromium.org,joedow@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1048774
Change-Id: I3063609e5a8f7f16e791222fe1782f28a3e37ac6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2042537Reviewed-by: Gary Kacmarcik <garykac@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Commit-Queue: Gary Kacmarcik <garykac@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739169}

remoting/host/basic_desktop_environment.cc

@@ -97,12 +97,12 @@ uint32_t BasicDesktopEnvironment::GetDesktopSessionId() const {
 std::unique_ptr<DesktopAndCursorConditionalComposer>
 BasicDesktopEnvironment::CreateComposingVideoCapturer() {
 #if defined(OS_MACOSX)
-  // Mac includes the mouse cursor in the captured image in curtain mode.
-  if (options_.enable_curtaining())
-    return nullptr;
-#endif
+  // MacOS always includes the mouse cursor in the captured image.
+  return nullptr;
+#else
   return std::make_unique<DesktopAndCursorConditionalComposer>(
       CreateVideoCapturer());
+#endif
 }
 
 std::unique_ptr<webrtc::DesktopCapturer>