asv: remove distances.DistancesBench.time_contact_matrix_sparse 10,000 benchmark

[orbeckst]

Expected behavior

All ASV benchmarks for the latest develop run (see benchmarks.benchmarks for the code and the MDAnalysis/benchmarks repo + the benchmarks wiki for more details.)

Actual behavior

The distances.DistancesBench.time_contact_matrix_sparse test times out as shown below (recent output from nightly run on Python 3.6).

[ 82.69%] ··· ...es.DistancesBench.time_contact_matrix_sparse         1/4 failed
[ 82.69%] ··· =========== ============
              num_atoms              
             ----------- ------------
                  10       396±2μs   
                 100      36.9±0.2ms 
                 1000     3.79±0.01s 
                10000       failed   
             =========== ============

[ 82.69%] ···· For parameters: 10000


              asv: benchmark timed out (timeout 60.0s)

We can either speed up the benchmark (not sure how as this is might be due to slow sparse matrix routines), reduce the size, or remove it (easiest option).