CMake: Remove cotire dependency

CMake now has native unity build support:
https://cmake.org/cmake/help/latest/variable/CMAKE_UNITY_BUILD.html

COPYRIGHT

@@ -11,10 +11,6 @@ Comment: The copyright of individual contributors is documented in the
   Git history.
 License: LGPL-3.0-only
 
-Files: cmake/cotire.cmake
-Copyright: 2012-2018 Sascha Kratky
-License: COTIRE
-
 Files: extern/googletest
 Copyright: 2008, Google Inc.
 License: GOOGLE
@@ -30,28 +26,6 @@ License: MIT
 License: LGPL-3.0-only
   [see LICENSE file]
 
-License: COTIRE
-  Permission is hereby granted, free of charge, to any person
-  obtaining a copy of this software and associated documentation
-  files (the "Software"), to deal in the Software without
-  restriction, including without limitation the rights to use,
-  copy, modify, merge, publish, distribute, sublicense, and/or sell
-  copies of the Software, and to permit persons to whom the
-  Software is furnished to do so, subject to the following
-  conditions:
-
-  The above copyright notice and this permission notice shall be
-  included in all copies or substantial portions of the Software.
-
-  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
-  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
-  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
-  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
-  OTHER DEALINGS IN THE SOFTWARE.
-
 License: GOOGLE
   Copyright 2008, Google Inc.
   All rights reserved.