main/mapbox-gl-native: upgrade to 1.6.0

Fix previous version not building anymore, as seen on v21.03 branch: https://builds.sr.ht/~postmarketos/job/433826

Just submitting @PureTryOut's work as MR. Shall be backported to v21.03 after merge.

I've bumped the pkgrels of mapbox-gl-qml and pure-maps, I guess they would break otherwise.

The resulting pure-maps build should be tested before merging this.

EDIT: pure-maps and its two depends are the last blockers for the initial build of v21.03 for x86_64. I've temporarily removed these three packages for now, let's rever the commit that removed them and cherry pick the MR once it's in master to get it back.