linux: remove redundant SDT tracepoints

Remove all the 'entry' and 'return' probes; they clutter up the source
and are redundant to FBT.

Reviewed By: dchagin
Sponsored By: EPSRC
Differential Revision: https://reviews.freebsd.org/D30040

(cherry picked from commit 5e8caee259d0cc73301b8fc60c8fb388e7f745af)