scripts: remove unnecessary ihex2fw and check-lc_ctypes from .gitignore

Commit c512d254 ("gitignore: ignore scripts/ihex2fw") was unneeded.
ihex2fw was generated in firmware/ instead of scripts/ at that time
although ihex2fw.c was pushed back and forth between those directories
in the past.

check-lc_ctype was removed by commit cb43fb57

 ("docs: remove
DocBook from the building system").

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>