test: Split `qsqlquery' unit and benchmark test

Moving benchmark test from 'tests/auto' to 'tests/benchmarks'.
Also removing 'qttest_p4' usage while we are at it.

- void benchmark();

was moved to 'tests/benchmarks/sql/kernel/qsqlquery'

Task-number: QTQAINFRA-353
Change-Id: I241bb1a2fba1c1b5524c21e5941a6c5daf5a4a89
Reviewed-by: Honglei Zhang <honglei.zhang@nokia.com>