remove redundant definition of cons2prim

[ranocha]

cons2prim is already defined in

Trixi.jl/src/equations/equations.jl

Lines 231 to 240 in 3ea50d1

	"""
	cons2prim(u, equations)
	Convert the conserved variables `u` to the primitive variables for a given set of
	`equations`. `u` is a vector type of the correct length `nvariables(equations)`.
	Notice the function doesn't include any error checks for the purpose of efficiency,
	so please make sure your input is correct.
	The inverse conversion is performed by [`prim2cons`](@ref).
	"""
	function cons2prim end

[sloede]

LGTM!