Strip byte-order mark from input_osk_utf8_pages.h to fix older GCC

[celerizer]

Old versions of GCC get hung up on this file because of the included BOM. As the file is UTF-8 the byte order is the same on every machine so this should be able to be safely removed.

This fixes the following error on old versions of GCC:

In file included from menu/menu_driver.c:62:
menu/../input/input_osk_utf8_pages.h:1: error: stray '\357' in program
menu/../input/input_osk_utf8_pages.h:1: error: stray '\273' in program
menu/../input/input_osk_utf8_pages.h:1: error: stray '\277' in program

See: https://www.unicode.org/versions/Unicode5.0.0/ch02.pdf

• Use of a BOM is neither required nor recommended for UTF-8, but may be encountered in contexts where UTF-8 data is converted from other encoding forms that use a BOM or where the BOM is used as a UTF-8 signature.