Replace compat.query.GetData()

It has been marked as deprecated since its addition by
Merlijn van Deen back in 2012 (commit
6dfa2cfff5e2f85cee51018250b92424b1ce751b).
The only bundled script using it, blockreview.py,
has been updated to use APISite.allusers() instead.

split from Gerrit change I7547897fd8719836c9eaa2a2b313c552e645a519

Change-Id: Idbb143835a2df1b8de994bb84631999a898d9dd4