package/bluez5_utils: Clean up descriptions

package/bluez5_utils: Clean up descriptions

The descriptions in this package have grown pretty confusing over time.
Try to make this a bit more consistent and up-to-date.

* drop references to old kernel versions not supported by BR anymore
* Remove "Bluez 5.x" string from options
* consistently use the term "plugin" (plugins implement profiles)
* make mentioned profile appreviations upper-case
* make descriptions closer to the ones in BlueZ Readme [0]
* make clear that "tests" refers to the python test scripts

[0] https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/README?h=5.58

Signed-off-by: Michael Nosthoff <buildroot@heine.tech>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[Arnout:
 - remove more 5.x references;
 - Use official spelling BlueZ in main help text]