pacific: doc/start/os-recommendations: drop 4.14 kernel and reword guidance

[zdover23]

The 4.14 LTS kernel has less than a year left in terms of maintenance, drop it.

Also, the current wording with an explicit list of kernels tends to go stale: it's missing the latest 6.1 LTS kernel.

Signed-off-by: Ilya Dryomov idryomov@gmail.com
(cherry picked from commit b697f96)

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