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

gdb/testsuite/gdb.base/catch-syscall.exp

@@ -348,9 +348,7 @@ proc test_catch_syscall_execve {} {
 	# Check for entry/return across the execve, making sure that the
 	# syscall_state isn't lost when turning into a new process.
 	insert_catch_syscall_with_arg "execve"
-
-	# Check that the execve is called.
-	check_call_to_syscall "execve"
+	check_continue "execve"
 
 	# Continue to main so extended-remote can read files as needed.
 	# (Otherwise that "Reading" output confuses gdb_continue_to_end.)