patch 8.2.0271: the "num64" feature is available everywhere

Problem:    The "num64" feature is available everywhere and building without
            it causes problems.
Solution:   Graduage the "num64" feature. (James McCoy, closes #5650)
diff --git a/src/testdir/test_largefile.vim b/src/testdir/test_largefile.vim
index 1b3e02a..68d6ec9 100644
--- a/src/testdir/test_largefile.vim
+++ b/src/testdir/test_largefile.vim
@@ -24,11 +24,6 @@
   w
   " Check if the file size is 4,000,000,000 bytes.
   let fsize=getfsize(fname)
-  if has('num64')
-    call assert_true(fsize == 4000000000)
-  else
-    " getfsize() returns -2 if a Number is 32 bits.
-    call assert_true(fsize == -2)
-  endif
+  call assert_true(fsize == 4000000000)
   call delete(fname)
 endfunc