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: I49fec5b9521f292df38c54bf5ddcb993d2e13d5c

openstack/manila,openstack/manila