Merge handle_inferior_event and handle_inferior_event_1

Merge handle_inferior_event and handle_inferior_event_1

I noticed that handle_inferior_event is just a small wrapper that
frees the value chain.  This patch replaces it with a
scoped_value_mark, reducing the number of lines of code here.

Regression tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-03-20  Tom Tromey  <tromey@adacore.com>

	* infrun.c (handle_inferior_event): Rename from
	handle_inferior_event_1.  Create a scoped_value_mark.
	(handle_inferior_event): Remove.