Fix memory leak in dbus::ObjectManager::RemoveInterface

Fix memory leak in dbus::ObjectManager::RemoveInterface

D-Bus Object Manager proxy class was leaking PropertySet object instances
stored in properties_map when an interface was removed.

Make sure we delete the PropertySet before we remove the map entry.

BUG=472654
Committed: https://crrev.com/9a99965adab379a5965484a59334a80bc576e49e
Cr-Commit-Position: refs/heads/master@{#323544}

[Alex Vakulenko, 2015-04-01 23:56:17]

The CQ bit was checked by avakulenko@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-04-01 23:57:22]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1055713002/1

[commit-bot: I haz the power, 2015-04-01 23:57:23]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-04-01 23:57:24]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Alex Vakulenko, 2015-04-01 23:57:31]

avakulenko@chromium.org changed reviewers:
+ keybuk@chromium.org

[keybuk, 2015-04-02 17:10:06]

lgtm

[Alex Vakulenko, 2015-04-02 17:10:21]

The CQ bit was checked by avakulenko@chromium.org

[commit-bot: I haz the power, 2015-04-02 17:11:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1055713002/1

[commit-bot: I haz the power, 2015-04-02 18:51:43]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-03 20:28:14]

Patchset 1 (id:??) landed as
https://crrev.com/9a99965adab379a5965484a59334a80bc576e49e
Cr-Commit-Position: refs/heads/master@{#323544}