Partially revert "Disable msvc vectorization in GC get_promoted_bytes (…

…dotnet#100309)" (dotnet#101995)

(commit 765ca4e)

Revert workaround but leave test in place.

src/coreclr/gc/gc.cpp

@@ -24247,9 +24247,6 @@ size_t gc_heap::get_promoted_bytes()
 
     dprintf (3, ("h%d getting surv", heap_number));
     size_t promoted = 0;
-#ifdef _MSC_VER
-#pragma loop(no_vector)
-#endif
     for (size_t i = 0; i < region_count; i++)
     {
         if (survived_per_region[i] > 0)