Remove old VRP jump threader code.
There's a lot of code that melts away without the ASSERT_EXPR based jump
threader. Also, I cleaned up the include files as part of the process.
gcc/ChangeLog:
* tree-vrp.c (lhs_of_dominating_assert): Remove.
(class vrp_jt_state): Remove.
(class vrp_jt_simplifier): Remove.
(vrp_jt_simplifier::simplify): Remove.
(class vrp_jump_threader): Remove.
(vrp_jump_threader::vrp_jump_threader): Remove.
(vrp_jump_threader::~vrp_jump_threader): Remove.
(vrp_jump_threader::before_dom_children): Remove.
(vrp_jump_threader::after_dom_children): Remove.