This ensures that we use the correct specialized variable at the call
site of a function. In #2725 what happened was that a generalized
function was aliased, causing it to undergo generalization again. Then,
we lost the variable used to specialize at the call site. Instead, just
link to the partial proc being aliased directly.
There is an added benefit here, which is that we can avoid the
possibly-quadratic replacement of symbols in the generated statement.
Closes#2725
