delete some of the parent object (ring) printing code

[tthsqe12]

In connection with Nemocas/AbstractAlgebra.jl#887, it would be nice not to have, for example, the following pointless duplication

Nemo.jl/src/flint/fmpz_mpoly.jl

Lines 283 to 300 in d530e05

	function show(io::IO, p::FmpzMPolyRing)
	local max_vars = 5 # largest number of variables to print
	n = nvars(p)
	print(io, "Multivariate Polynomial Ring in ")
	if n > max_vars
	print(io, nvars(p))
	print(io, " variables ")
	end
	for i = 1:min(n - 1, max_vars - 1)
	print(io, string(p.S[i]), ", ")
	end
	if n > max_vars
	print(io, "..., ")
	end
	print(io, string(p.S[n]))
	print(io, " over ")
	show(io, base_ring(p))
	end

There is minimal required interface to get this working generically.

[wbhart]

I'm afraid I have no idea what you mean, or how it is related to 887.

I will do MPoly last, but I am not putting any major effort into it at this time. I would like to make an abstract interface for MPolys, but it's not something I'm doing for that PR.

[tthsqe12]

What I mean is: once symbols and coefficient_ring are implemented, the printing can be implemented generically in terms of this required interface. There is no need for all of this code duplication.

[fingolfin]

This one has been resolved quite some time ago in PR #1438