Remove ptid_equal

Remove ptid_equal in favor of using "==".

gdb/ChangeLog
2018-07-03  Tom Tromey  <tom@tromey.com>

	* common/ptid.c (ptid_equal): Remove.
	* common/ptid.h (ptid_equal): Don't declare.
	* ada-tasks.c: Update.
	* breakpoint.c: Update.
	* common/agent.c: Update.
	* corelow.c: Update.
	* darwin-nat-info.c: Update.
	* darwin-nat.c: Update.
	* dcache.c: Update.
	* dtrace-probe.c: Update.
	* dummy-frame.c: Update.
	* fbsd-nat.c: Update.
	* frame.c: Update.
	* gdbthread.h: Update.
	* gnu-nat.c: Update.
	* go32-nat.c: Update.
	* inf-loop.c: Update.
	* inf-ptrace.c: Update.
	* infcall.c: Update.
	* infcmd.c: Update.
	* inflow.c: Update.
	* infrun.c: Update.
	* linux-fork.c: Update.
	* linux-nat.c: Update.
	* linux-thread-db.c: Update.
	* mi/mi-cmd-var.c: Update.
	* mi/mi-interp.c: Update.
	* mi/mi-main.c: Update.
	* nto-procfs.c: Update.
	* ppc-linux-tdep.c: Update.
	* procfs.c: Update.
	* python/py-inferior.c: Update.
	* python/py-record-btrace.c: Update.
	* python/py-record.c: Update.
	* ravenscar-thread.c: Update.
	* regcache.c: Update.
	* remote-sim.c: Update.
	* remote.c: Update.
	* sol-thread.c: Update.
	* solib.c: Update.
	* target.c: Update.
	* tui/tui-stack.c: Update.
	* varobj.c: Update.
	* windows-nat.c: Update.
	* windows-tdep.c: Update.

gdb/gdbserver/ChangeLog
2018-07-03  Tom Tromey  <tom@tromey.com>

	* linux-low.c: Update.
	* lynx-low.c: Update.
	* mem-break.c: Update.
	* nto-low.c: Update.
	* remote-utils.c: Update.
	* server.c: Update.
	* spu-low.c: Update.
	* target.c: Update.
	* win32-low.c: Update.

gdb/linux-thread-db.c

@@ -1792,7 +1792,7 @@ thread_db_target::resume (ptid_t ptid, int step, enum gdb_signal signo)
 {
   struct thread_db_info *info;
 
-  if (ptid_equal (ptid, minus_one_ptid))
+  if (ptid == minus_one_ptid)
     info = get_thread_db_info (inferior_ptid.pid ());
   else
     info = get_thread_db_info (ptid.pid ());