Fix for gdb.server/non-existing-program.exp test case

The last commit was supposed to have the reference to ptrace () removed.
The patch didn't get updated correctly before the commit.  This commit
fixes the comment as requested

gdbserver/ChangeLog

	2016-09-06  Carl Love  <cel@us.ibm.com>

	* server.c (start_inferior):  Fixed comment, requested comment change
	didn't get updated correctly.  Removed reference to ptrace () call as
 	it is only true on Linux systems.