databases/pointcloud: Rework Makefile and remove libght dependency

Rework Makefile to follow Porters Handbook more closely
Remove non needed variable
Remove libght dependency, this was removed in 1.2.0

Reference:
https://github.com/pgpointcloud/pointcloud/blob/v1.2.0/NEWS

PR: 264184
Approved by: lbartoletti (maintainer timeout, 4+ weeks)