require CMake version 3.10. remove tests for older versions.

cmake/Modules/Packages/GPU.cmake

@@ -1,7 +1,4 @@
 if(PKG_GPU)
-    if (CMAKE_VERSION VERSION_LESS "3.1")
-      message(FATAL_ERROR "For the GPU package you need at least cmake-3.1")
-    endif()
     set(GPU_SOURCES_DIR ${LAMMPS_SOURCE_DIR}/GPU)
     set(GPU_SOURCES ${GPU_SOURCES_DIR}/gpu_extra.h
                     ${GPU_SOURCES_DIR}/fix_gpu.h

cmake/Modules/Packages/LATTE.cmake

@@ -8,9 +8,6 @@ if(PKG_LATTE)
   endif()
   option(DOWNLOAD_LATTE "Download the LATTE library instead of using an already installed one" ${DOWNLOAD_LATTE_DEFAULT})
   if(DOWNLOAD_LATTE)
-    if (CMAKE_VERSION VERSION_LESS "3.7") # due to SOURCE_SUBDIR
-      message(FATAL_ERROR "For downlading LATTE you need at least cmake-3.7")
-    endif()
     if(CMAKE_GENERATOR STREQUAL "Ninja")
       message(FATAL_ERROR "Cannot build downloaded LATTE library with Ninja build tool")
     endif()

cmake/Modules/Packages/MSCG.cmake

@@ -8,9 +8,6 @@ if(PKG_MSCG)
   endif()
   option(DOWNLOAD_MSCG "Download MSCG library instead of using an already installed one)" ${DOWNLOAD_MSCG_DEFAULT})
   if(DOWNLOAD_MSCG)
-    if (CMAKE_VERSION VERSION_LESS "3.7") # due to SOURCE_SUBDIR
-      message(FATAL_ERROR "For downlading MSCG you need at least cmake-3.7")
-    endif()
     if(CMAKE_GENERATOR STREQUAL "Ninja")
       message(FATAL_ERROR "Cannot build downloaded MSCG library with Ninja build tool")
     endif()

cmake/Modules/Packages/USER-MOLFILE.cmake

@@ -1,8 +1,4 @@
 if(PKG_USER-MOLFILE)
-  if (CMAKE_VERSION VERSION_LESS "3.10") # due to INTERFACE without a library
-    message(FATAL_ERROR "For configuring USER-MOLFILE you need CMake 3.10 or later")
-  endif()
-
   set(MOLFILE_INCLUDE_DIRS "${LAMMPS_LIB_SOURCE_DIR}/molfile" CACHE STRING "Path to VMD molfile plugin headers")
   add_library(molfile INTERFACE)
   target_include_directories(molfile INTERFACE ${MOLFILE_INCLUDE_DIRS})