libusbg: Add internal free functions for each library structure.
libusbg: Add internal free functions for each library structure.

Library should have internal API for freing structures instead of
copy pasting same code in different places.

Signed-off-by: Krzysztof Opasiak <8064eda6f94b3817252b7d7649cf754592f63500@samsung.com>

pszewczyk/libusbg,pszewczyk/libusbg