Drop unused header file <ext/stdio_filebuf.h> from parser/libapparmor_re/aare_rules.cc

[Manoj Gupta]

parser/libapparmor_re/aare_rules.cc uses a GNU extension header file <ext/stdio_filebuf.h>
The extension features are unused. I am able to build apparmor by commenting out the header file include.

This header is no present on other c++ libraries e.g. libc++. As a consequence, apparmor cannot be built with libc++. Since the header file is unused, I request that this header be dropped so that apparmor does not have any build issues when libc++ is used as the c++ library.