Update help of the "frame" command

Update help of the "frame" command

The help message of the "frame" command states that nothing is printed
if the command is executed from the command file or user-defined
command.  My testing leads me to think that this is not true (at least
today).

  (gdb) bt
  #0  bar (n=17) at test.c:9
  #1  0x00000000004006e0 in foo (v=17) at test.c:13
  #2  0x00000000004006f0 in main () at test.c:21
  (gdb) frame
  #0  bar (n=17) at test.c:9
  9	    baz(n);
  (gdb) define foo
  Type commands for definition of "foo".
  End with a line saying just "end".
  >frame 1
  >end
  (gdb) foo
  #1  0x00000000004006e0 in foo (v=17) at test.c:13
  13	    bar(v);

This patch simply removes that bit from the help message.  I didn't find
anything corresponding to this in the documentation that needs to be
fixed.

The behavior change corresponding to this documentation change was done
in commit b00771232fab861fb31e42dfd5f6643ba1b43cc9.

gdb/ChangeLog:

	* stack.c (_initialize_stack): Update "frame" command help message.