fix gpu_tests option usage

Author: Daniel Limberger

source/tests/CMakeLists.txt

@@ -8,11 +8,6 @@ if(NOT OPTION_BUILD_TESTS)
     return()
 endif()
 
-if(NOT OPTION_BUILD_GPU_TESTS)
-    return()
-endif()
-
-
 # DISABLE CMP0037: Target names should not be reserved and should match a validity pattern.
 cmake_policy(SET CMP0037 OLD)