[prefix] Remove impossible progress message

The "progress" macro can be used only from within the .prefix section.
At the point of calling relocate(), we are running in .text16 and so
the near call to print_message() will end up calling a random function
somewhere in .text16.

Interestingly, this problem has remained unnoticed for some time.  It
is rare to build with DEBUG=libprefix.  In the few cases that it has
been used during development, the randomly selected function in
.text16 seems to have been a harmless no-op with no visible
side-effects (beyond the unnoticed failure to print the "relocate"
progress message).

Fix by removing the futile attempt to print a progress message before
calling relocate().

Reported-by: Raed Salem <raeds@mellanox.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/prefix/libprefix.S

 	 * relocate() will return with %esi, %edi and %ecx set up
 	 * ready for the copy to the new location.
 	 */
-	progress "  relocate\n"
 	virtcall relocate
 
 	/* Jump back to .prefix segment */