Remove path_range_query constructor that takes an edge.

Remove path_range_query constructor that takes an edge.

The path_range_query constructor that takes an edge is really a
convenience function for the loop-ch pass.  It feels wrong to pollute
the API with such a specialized function that could be done with
a small inline function closer to its user.

As an added benefit, we remove one use of reset_path.  The last
remaining one is the forward threader one.

Tested, thread-counted, and benchmarked on x86-64 Linux.

gcc/ChangeLog:

	* gimple-range-path.cc (path_range_query::path_range_query):
	Remove constructor that takes edge.
	* gimple-range-path.h (class path_range_query): Same.
	* tree-ssa-loop-ch.cc (edge_range_query): New.
	(entry_loop_condition_is_static): Call edge_range_query.