Fixed bug in hydrogen atom removal in molecule drawing algorithm.
Fixed bug in hydrogen atom removal in molecule drawing algorithm.

The bug occurred when deleting from a dict that was currently being iterated
over, which is a no-no. A quick refactoring takes care of this.

nyee/RMG-Py,enochd/RMG-Py,nickvandewiele/RMG-Py,chatelak/RMG-Py,chatelak/RMG-Py,KEHANG/RMG-Py,faribas/RMG-Py,pierrelb/RMG-Py,nyee/RMG-Py,comocheng/RMG-Py,nickvandewiele/RMG-Py,comocheng/RMG-Py,KEHANG/RMG-Py,faribas/RMG-Py,pierrelb/RMG-Py,jwallen/ChemPy,enochd/RMG-Py