vim: remove unneeded cross flag

> This doesn't seem to be needed for recent autoconf

pkgs/applications/editors/vim/default.nix

···
     "vim_cv_tty_mode=0660"
     "vim_cv_getcwd_broken=no"
     "vim_cv_stat_ignores_slash=yes"
-    "ac_cv_sizeof_int=4"
-    "vim_cv_memmove_handles_overlap=yes"
     "vim_cv_memmove_handles_overlap=yes"
   ];