Revert (part of) "gdb fix for catch-syscall.exp"

Revert (part of) "gdb fix for catch-syscall.exp"

This reverts (par of) commit ab198279120fe7937c0970a8bb881922726678f9.
This commit changed what the test expects when catching the execve
syscall based on the behavior seen on a Linux PowerPC machine.  That is,
we get an "entry" event, but no "return" event.  This is not what we get
on Linux with other architectures, though, and it seems like a
PowerPC-specific bug.

Revert the part of the patch related to this, but not the other hunk.

Change-Id: I4248776e4299f10999487be96d4acd1b33639996