staging: wilc1000: remove wilc_exported_buf.c

The config option, CONFIG_WILC1000_PREALLOCATE_DURING_SYSTEM_BOOT, was
never able to be set, so this file was never being built.  Also, as
WILC_PREALLOC_AT_BOOT was never being set in the build system, remove
all code framed by that symbol.

Cc: Johnny Kim <johnny.kim@atmel.com>
Cc: Rachel Kim <rachel.kim@atmel.com>
Cc: Dean Lee <dean.lee@atmel.com>
Cc: Chris Park <chris.park@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>