[Applet/TaskManager]Don't create extra PulseAudio component

Summary: Use the component already created.

Test Plan:
Functionality must stay the same.
Test with D27684's Test Plan.
Also test without plasma-pa, no options or icon should appear,
without any warning.

Reviewers: #plasma, hein, ngraham

Reviewed By: ngraham

Subscribers: broulik, ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D27734