Drop support for SQLite < 3.7
Drop support for SQLite < 3.7

Both Ubuntu 18.04 [1] and CentOS 8 [2] provide sufficiently new versions
of SQLite that make this check unnecessary now.

[1] https://packages.ubuntu.com/bionic/sqlite3
[2] http://mirror.centos.org/centos/7/os/x86_64/Packages/

Change-Id: I096e673319663f539788f27fdf056ad10153f6bf

openstack/cinder,mahak/cinder,openstack/cinder,mahak/cinder