doc/distributions: don't mention Fedora version

Don't mention specific Fedora version. We'd have
to constantly keep updating this every time Fedora
gets an update.

Signed-off-by: Karol Latecki <karol.latecki@intel.com>
Change-Id: Ibb9093d106554a8d244b75ae83f627a093f729b9
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/16660


Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Michal Berger <michal.berger@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>