Discontinuities get detected beyond the specified time interval =>IndexError

[YannickNoelStephanKuhn]

Describe the bug
If the solver detects discontinuities beyond the timepoints "t_eval" as in "solver.solve(model, t_eval)", it will try to insert them at the end, throwing an IndexError when accessing the index after the last entry in "t_eval".

To Reproduce
Steps to reproduce the behaviour:
0. Optional: pybamm.set_logging_level("INFO") to check if discontinuities got detected.

1. Load up a default set-up of a DFN-model and CasADi-solver.
2. Specify a charge pulse profile like so:
   pulse_currents = [current_0, current_1]
   pulse_timespans = [[t_0_l, t_0_r], [t_1_l, t_1_r]]
   def current_function(time):
   return_value = 0
   for current, timespan in zip(pulse_currents, pulse_timespans):
   return_value = return_value + current * ((timespan[0] < time) * (time < timespan[1]))
   return return_value
   parameters["Current function [A]"] = current function
3. Set a short time interval: t_eval = np.linspace(t_0_l - eps, t_0_r, 100) with eps>0.
4. Get the IndexError:
   File "/usr/local/lib/python3.7/dist-packages/pybamm/solvers/base_solver.py", line 556, in solve
   if dtime - eps < t_eval_dimensionless[dindex] < dtime + eps:
   IndexError: index 104 is out of bounds for axis 0 with size 104

Expected behaviour
If a discontinuity lies beyond the requested time interval "t_eval", it should be treated as if it wouldn't exist. For efficiency and stability, there shouldn't be any checks for discontinuities beyond "t_eval".

[valentinsulzer]

So this should just be a case of removing any discontinuities that are greater than t_eval? For example, just after we remove any identical discontinuities?