Remove cmake_minimum_required from DownloadProject configuration

We already have a top-level minimum requirement for CMake >= 3.8, so
don't need to specific that requirement in a file included from the top
level.

Having a requirement as low as 2.8.2 broke building on newer version of
CMake, which error with "Compatibility with CMake < 3.5 has been removed
from CMake." (seen in GitHub runners with Ubuntu 24.04).

Author: tautschnig

cmake/DownloadProject.CMakeLists.cmake.in

@@ -1,8 +1,6 @@
 # Distributed under the OSI-approved MIT License.  See accompanying
 # file LICENSE or https://github.com/Crascit/DownloadProject for details.
 
-cmake_minimum_required(VERSION 2.8.2)
-
 project(${DL_ARGS_PROJ}-download NONE)
 
 include(ExternalProject)