Fix wxFileSystemWatcher::RemoveAll() to actually work.

We need to call DoRemove() on all watcher objects to really remove them, just
removing our record of them was not enough and e.g. resulted in errors if we
tried to re-add a previously watched path again.

Closes #15531.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76182 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -583,6 +583,7 @@ All:
 - Fix wxSocket::WaitForAccept() in non-main thread (Hajo Kirchhoff).
 - Fix memory overallocation in wxVector::reserve() (Nigel Paton).
 - Fix `wx-config --libs` in monolithic build.
+- Fix wxFileSystemWatcher::RemoveAll() (Melroy Tellis).
 - Fix the build under HP-UX (tested under 11.31).
 - Add Aragonese translation.