Remove check for homogeneous array

[sethcall]

In conformance with latest TOML spec...

[ksunden]

My reading of the code indicates that with this change atype is not at all used anywhere and so the variable can simply be removed entirely (and then also ntype for that matter (i.e. doing nval, _ = self.load_value(a[i]) to indicate that the returned value is not used))

[zoj613]

ping @uiri