jl_ is no longer exported

[mkitti]

Currently jl_ is used here:

pyjulia/src/julia/libjulia.py

Lines 34 to 35 in 87c669e

	libjulia.jl_.argtypes = [c_void_p]
	libjulia.jl_.restype = None

However, jl_ is no longer exported by libjulia[-internal]:
#437 (comment)
JuliaLang/julia#40246 (comment)