WL#9581: Deprecate and remove DTrace probes

This work removes the DTrace probes in MySQL.

The probes were added in 2008, as a backport from MySQL 6.0. There are a few
very basic probes (e.g. number of rows fetched  and number of index lookups);
there has been little activity nor user requests to add more.

DTrace probes have shown to be a steady source of build breaks and other issues
that need engineering time, complicates the build system, and works as an
impediment to cleanups. In particular, DTrace probes are not compiled through
the normal build system but through a special set of scripts, and interact with
linking in complicated ways. These interactions are different from platform to
platform, multiplying the maintenance cost.

We know of no immediate way to give a warning when a DTrace probe is used. Thus,
the recommendation would be to just remove them outright with no deprecation period.


User Documentation
==================

* http://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-18.html
* http://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-1.html
* http://dev.mysql.com/doc/refman/5.7/en/mysql-nutshell.html
* http://dev.mysql.com/doc/refman/8.0/en/mysql-nutshell.html