simplify static linking implementation
We've long used darshan-stubs library and some
--undefined=symbol ld-opts in Darshan's static linking cases, perhaps just to work around some strange linking issues from Crays from years ago. In recent testing of the new HDF5 module in static linking cases, I don't see any ill effects from completely removing the use of these mechanisms. This MR removes the stubs library and the extraneous ld-opts, simplifying Darshan's static instrumentation methodology.
I've left as a WIP until I've tested on Theta, which would verify we still get this right on Crays. Works fine on my laptop across a range of test cases, including when using higher level I/O libary like HDF5.