Re-disable vendoring of cli11 by default (#179)

Revert "Restore vendoring of cli11 by default (#178)"
This reverts commit bdcef68.

Signed-off-by: Steve Peters <[email protected]>

Author: scpeters

CMakeLists.txt

@@ -25,7 +25,7 @@ gz_configure_project(VERSION_SUFFIX pre1)
 option(
   GZ_UTILS_VENDOR_CLI11
   "If true, use the vendored version of CLI11, otherwise use an external one"
-  ON)
+  OFF)
 
 #============================================================================
 # Search for project-specific dependencies

Migration.md

@@ -7,12 +7,10 @@ release will remove the deprecated code.
 
 ## Gazebo Utils 3.X to 4.X
 
-<!--
 The default value of `GZ_UTILS_VENDOR_CLI11` is now set to `OFF`, so that
 an external version of `cli11` will be preferred by default. This is in
 preparation to remove the vendored version (see
 [issue #135](https://github.com/gazebosim/gz-utils/issues/135)).
--->
 
 ## Gazebo Utils 2.X to 3.X