LU-11720 spec: srpm should be free of kernel requiements

LU-11720 spec: srpm should be free of kernel requiements

This moves the fix for LU-9731 into spec file and out of lbuild.
This lets "make rpms" benefit from the fix.
This also prevents the srpm from being incorrectly locked to the
kernel present when lbuild was used to create it (via
kmp-lustre.preamble).

Test-Parameters: trivial
Signed-off-by: Nathaniel Clark <nclark@whamcloud.com>
Change-Id: I15f61c0e37182c0efbea3566d43b1e89f180d3e5
Reviewed-on: https://review.whamcloud.com/33771
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Gu Zheng <gzheng@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>