KNOWN_BUGS: fixed "USE_UNIX_SOCKETS on Windows"

Fixed with #5170 (commit 23a870f2fd041278)
diff --git a/docs/KNOWN_BUGS b/docs/KNOWN_BUGS
index 9b7be5f..cd4990c 100644
--- a/docs/KNOWN_BUGS
+++ b/docs/KNOWN_BUGS
@@ -48,7 +48,6 @@
  4.5 Improve --data-urlencode space encoding
 
  5. Build and portability issues
- 5.1 USE_UNIX_SOCKETS on Windows
  5.2 curl-config --libs contains private details
  5.3 curl compiled on OSX 10.13 failed to run on OSX 10.10
  5.4 Cannot compile against a static build of OpenLDAP
@@ -361,13 +360,6 @@
 
 5. Build and portability issues
 
-5.1 USE_UNIX_SOCKETS on Windows
-
- Due to incorrect CMake checks for the presence of the feature, it will never
- be enabled for windows in a cmake build.
-
- See https://github.com/curl/curl/issues/4040
-
 5.2 curl-config --libs contains private details
 
  "curl-config --libs" will include details set in LDFLAGS when configure is