contrib: modernize gen_autofdo_event.py

contrib: modernize gen_autofdo_event.py

Python 2 has been EOL'ed for two years.  egrep has been deprecated
for many years and the next grep release will start to print warning if
it is used.

-E option may be unsupported by some non-POSIX grep implementations, but
gcc-auto-profile won't work on non-Linux systems anyway.

contrib/ChangeLog:

	* gen_autofdo_event.py: Port to Python 3, and use grep -E
	instead of egrep.

gcc/ChangeLog:

	* config/i386/gcc-auto-profile: Regenerate.