staging: rtl8188eu: remove unused members from struct recv_priv

Since commit da25a8ec ("staging: rtl8188eu: remove unused
debugging functions") is_signal_dbg is never set to true, so the code
under if (adapter->recvpriv.is_signal_dbg) is dead. Remove the
variable and the dead code.

The signal_strength_dbg was referenced only in the code that is being
removed, so remove it as well.

Also fix coding style issues in the touched lines.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Ivan Safonov <insafonov@gmail.com>
Cc: devel@driverdev.osuosl.org
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>