Updated erase function in SlipPlane::dislocation_dislocationInteraction.
The erase function removed the element before last. This caused a
segmentation fault when later the defects are swept for stressField as
the defect was pointing to an empty memory location.
Deleting items in SlipPlane::dislocations as a block.
Earlier the dislocations were deleted one by one. This led to the
iterators being invalid once an earlier dislocation was removed. This is
countered by deleting the dislocations in a single block using a call of
type erase(first, last).