Several of the test cases in perf_fast_forward do not need
partition-level fast-forwarding. However, since the defaults are used to
construct most of the readers the fast-forwarding is enabled regardless.
This showed an apparent regression in the perf_fast_forward results
after adcb3ec20c ("row_cache: read is not
single-partition if inter-partition forwarding is enabled") which
disabled an optimisation that was invalid when partition-level
fast-forwarind was requested.
This patch ensures that all single-partition reads that do not need
partition-level fast-forwarding keep it disabled.
5d5777f85e