i#690 mod pending tree: remove pending due to first-exec modload event
i#690 mod pending tree: remove pending due to first-exec modload event

With DRi#884's module load event triggering on first execution instead of
first map, we no longer need the module pending tree from i#690.

Review-URL: https://codereview.appspot.com/221460043

sigma-random/drmemory,sigma-random/drmemory,code4bones/drmemory,sigma-random/drmemory,LohithBlaze/drmemory,code4bones/drmemory,sigma-random/drmemory,LohithBlaze/drmemory,code4bones/drmemory,code4bones/drmemory,sigma-random/drmemory,LohithBlaze/drmemory,code4bones/drmemory,LohithBlaze/drmemory,LohithBlaze/drmemory