ada-lang.c: Really include "ui-out.h".

ada-lang.c: Really include "ui-out.h".

Currently, ada-lang.c pretends to include "ui-out.h" as follow:

    #ifdef UI_OUT
    #include "ui-out.h"
    #endif

However, UI_OUT is never defined as far as I can tell. This is confirmed
by rebuilding with a #error pragma inside the #ifdef UI_OUT block,
which never triggers.

Since this unit makes references to declarations from ui-out.h,
this patch simply removes the #ifdef/#endif condition.  This has not
been an error so far because "ui-out.h" indirectly gets included,
via one of the other .h files being included.

gdb/ChangeLog:

        * ada-lang.c: Remove "#ifdef UI_OUT" condition for including
        "ui-out.h".