staging: r8188eu: remove rtw_usleep_os

Remove the rtw_usleep_os helper function. There are only two callers, both
of which call rtw_usleep_os(100). This is equivalent to msleep(1).

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Tested-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220626180603.287054-1-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>