python: remove dtrace vestiges

Homebrew used to optionally build DTrace support via a patch [0]. The
patch was removed in `39848385`, but support for passing along the
`--with-dtrace` option the patch provided was not.

This config option is nonsense without the patch; remove it to avoid
disappointing DTrace-seeking folks like me.

[0]: http://bugs.python.org/issue13405

Closes #35177.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>