mac: Make build_app_dmg more silent.

mac: Make build_app_dmg more silent.

1.) Remove `set -x`
2.) Explicitly add '.dmg' extension to output, so pkg-dmg no longer
    warns about adding this implicitly
3.) Pass '--verbosity 0' to pkg-dmg to tell it to print only errors

If build_app_dmg needs to be debugged, it's easy to undo 1 and 3.
There's no need to have all this output on every single build.

BUG=none
TEST=`ninja all` has 38 lines less output.


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=132424

[Mark Mentovai, 2012-04-16 15:30:33]

LGTM

[commit-bot: I haz the power, 2012-04-16 16:12:40]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/thakis@chromium.org/10073020/1

[commit-bot: I haz the power, 2012-04-16 17:48:41]

Change committed as 132424