Revert "CMake: reduce required cmake version to 3.16 to support older CircleCI images until openSSL 3 support has arrived"

This reverts commit 6a309a2e05.

CMakeLists.txt

@@ -8,7 +8,7 @@
 # WITHOUT ANY WARRANTY, to the extent permitted by law; without even the
 # implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 
-cmake_minimum_required(VERSION 3.16)
+cmake_minimum_required(VERSION 3.18)
 
 # add this options before PROJECT keyword
 set(CMAKE_DISABLE_SOURCE_CHANGES ON)