algo: Remove span typedefs from Prelude.h

Changes were discussed in todays Online Meeting

algo/base/Prelude.h

@@ -5,7 +5,6 @@
 #define CBM_ALGO_BASE_PRELUDE_H
 
 #include <cstdint>
-#include <gsl/span>
 
 namespace cbm::algo
 {
@@ -28,14 +27,6 @@ namespace cbm::algo
   using real = f32;
 #endif
 
-#if !XPU_IS_CUDA && !XPU_IS_HIP  // FIXME why doesn't this work with CUDA?
-  template<typename T>
-  using span = gsl::span<T>;
-
-  template<typename T>
-  using cspan = gsl::span<const T>;
-#endif
-
 }  // namespace cbm::algo
 
 #endif  // CBM_ALGO_BASE_PRELUDE_H