Use the expression angle units while simplifying it

Use the expression angle units while simplifying it

Don't use the angle mode, use the angle units included
in the expression instead (Bug#23889).
* lisp/calc/calc-alg.el (calc-input-angle-units): New defun.
(math-simplify): Use it.
* lisp/calc/calc-forms.el (math-to-hms, math-from-hms):
Don't use calc-angle-mode if math-simplifying-units is non-nil.
* lisp/calc/calc-math.el (calcFunc-nroot, math-from-radians)
(math-to-radians-2, math-from-radians-2): Don't convert angle
to radians if math-simplifying-units is non-nil.
* test/lisp/calc/calc-tests.el (test-calc-23889): Add test.