Revert "LU-4413 osp: move seq allocation out of osp_import_event"

This reverts commit 01c06c7bf8c6b1b1468fac6b19f9572fc804198e.
Revert "LU-4456 osp: extra check for opd_pre"

This reverts commit 5a8f29612f4a0441ef26904890e31057a2eb2af5.
Revert "LU-3529 osp: init FID client for OSP on MDT."

This reverts commit 4be0f43980ff34d82a18c7dfcaa88474c3fceb80.