Remove recursion in simplify_control_stmt_condition_1 [PR114855].

Remove some ad-hoc simplification code in the forward threader, as the
call into the ranger in m_simplifier->simplify() will handle anything we
can do manually in simplify_control_stmt_condition_1.

In PR114855, DOM time is reduced from 120s to 92s (-23%) and overall
compilation time from 235s to 205s (-12%).  The total thread count at -O1 is
unchanged for the testcase.

In our bootstrap .ii benchmark suite, I see we thread 3 threads less
over all files at -O1.  At -O2, the backward threader picks up one more,
for no difference over all.

	PR tree-optimization/114855

gcc/ChangeLog:

	* tree-ssa-threadedge.cc: Remove unneeded recursion.