[PartialInlining] Enable recursive partial inlining.

It seems unnecessarily limiting to disallow recursive partial
inlining, and there are clearly cases where it can benefit
code by avoiding a function call and potentially enabling
other transformations like dead argument elimination
in cases where an argument is only used prior to the early-out
test at the top of the function.

The pass already properly rewrites the recursive calls
within the body of the freshly cloned function, so the only
change here is removing the bail-out when recursion is
detected.

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D136383