linux config: revert BPF_JIT_ALWAYS_ON=yes

This reverts a small bit of af808bd8 from PR #73328.  Fixes #79304:
tests.installer.simpleUefiSystemdBoot.x86_64-linux

I still don't know why the regression happened, but this feature doesn't
seem important enough to block channel now, though it reportedly helps
to mitigate spectre 2 attack CVE-2017-5715.