Remove call to gdb_flush at end of ada_val_print_1

Remove call to gdb_flush at end of ada_val_print_1

I am not sure why this function was called in the first place, but
it disrupts the printing flow when in GDB/MI mode, ending the current
console stream output, and starting a new one. It's not clear whether,
with the code as currently written, the problem is actually visible
or only latent. But, it becomes visible when we replace one of the
"return" statements in the "switch" block just above by a "break"
statement (this is something I'd like to do, and what made me realize
the problem). With the gdb_flush call (after having replaced the
"return" statement as explained above), we get:

        % gdb -q -i=mi ada_prg
        (gdb)
        print 1
        &"print 1\n"
  !! -> ~"$1 = 1"
  !! -> ~"\n"
        ^done

With the gdb_flush call removed, we now get the entire output into
a single stream.

        (gdb)
        print 1
        &"print 1\n"
        ~"$1 = 1"
        ~"\n"
        ^done

gdb/ChangeLog:

        * ada-valprint.c (ada_val_print_1): Remove call to gdb_flush.