Audio VTS: remove expectation of policy configuration unicity

The XML audio policy configuration is expected to be located in /vendor.
Additionally for AOSP builds (no vendor) and as a fallback in case of
missing vendor configuration, the system supports loading the XML from
/system.
This fallback config is not guaranty to be compatible with the phone HAL,
but probably does for a wide range of android phones
(at least for basic use cases).

In each of those cases, there is only one configuration file, either in
/vendor or /system.
As a result, the audio policy configuration VTS test was asserting that
only one audio_policy_configuration.xml could be found.
If multiple were found, one was useless and the platform integrator
should remove it.

But VTS are now run on phone with a /system partition from an AOSP
build and a /vendor partition from a device build.
In such scenario two audio policy config are now present on the device,
thus breaking the VTS expectation.

This is not a problem for the framework because it does not look for a /system
config if one was found in /vendor.

In the future, the /system XML might be removed as boards
specific config should be found in /vendor only as per treble
requirements.

Test: Compile
Bug: 65482614
Merged-In: I7cd7eb7284c0aa52782aa591411f8a9bf2a87a76
Change-Id: I7cd7eb7284c0aa52782aa591411f8a9bf2a87a76
Signed-off-by: Kevin Rocard <krocard@google.com>
(cherry picked from commit 76efe01b)