staging: r8188eu: Convert driver to use external firmware

As originally submitted, this driver acquired its firmware from data
statements embedded in the source code. This information has been extracted
into a binary file that has been accepted into the linux-firmware git
repo as commit ffc47f1 entitled "rtlwifi: Add new firmware files for
rtl8188eu". This patch switches the driver to use this file, and deletes
the firmware data from the source.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>