libaa have library but no `.h` header file on SDK

[brunvonlope]

On GIMP project we are starting to develop our official snap to further publishing on Snap Store.

But at build time on snapcraft we are needing to list libaa1-dev on build-packages: because there is no header file on the SDK

So, we should either remove libaa .so libraries from the SDK (since apt rdepends shows that no GNOME library depends on it) or, better(?), ship the .h files to help projects like GIMP and that use such dep so build easily without needing to install libaa1-dev.