Replace use of deprecated exec_program.

Silencing CMP0153 warnings.

cmake/cmake_uninstall.cmake.in

@@ -9,10 +9,10 @@ string(REGEX REPLACE "\n" ";" files "${files}")
 foreach(file ${files})
   message(STATUS "Uninstalling $ENV{DESTDIR}${file}")
   if(IS_SYMLINK "$ENV{DESTDIR}${file}" OR EXISTS "$ENV{DESTDIR}${file}")
-    exec_program(
-      "@CMAKE_COMMAND@" ARGS "-E remove \"$ENV{DESTDIR}${file}\""
+    execute_process(
+      COMMAND ${CMAKE_COMMAND} -E remove \"$ENV{DESTDIR}${file}\"
       OUTPUT_VARIABLE rm_out
-      RETURN_VALUE rm_retval
+      RESULT_VARIABLE rm_retval
       )
     if(NOT "${rm_retval}" STREQUAL 0)
       message(FATAL_ERROR "Problem when removing $ENV{DESTDIR}${file}")