Revert "merge: pass verbosity flag down to merge-recursive"

This reverts commit 2bf15a3, whose
intention was good, but the verbosity levels used in merge-recursive
turns out to be rather uneven.  For example, a merge of two branches
with conflicting submodule updates used to report CONFLICT: output
with --quiet but no longer (which *is* desired), while the final
"Automatic merge failed; fix conflicts and then commit" message is
still shown even with --quiet (which *is* inconsistent).

Originally reported by Bryan Turner; it is too early to declare what
the concensus is, but it seems that we would need to level the
verbosity levels used in merge strategy backends before we can go
forward.  In the meantime, we'd revert to the old behaviour until
that happens.

cf. $gmane/267245

builtin/merge.c

@@ -684,10 +684,6 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
 			o.subtree_shift = "";
 
 		o.renormalize = option_renormalize;
-		if (verbosity < 0)
-			o.verbosity = verbosity;
-		else if (verbosity > 0)
-			o.verbosity += verbosity;
 		o.show_rename_progress =
 			show_progress == -1 ? isatty(2) : show_progress;