Use default EA repr for IntervalArray

[jorisvandenbossche]

IntervalArray still has a custom repr:

In [41]: pd.arrays.IntervalArray.from_breaks(range(3))                                                                                                                          
Out[41]: 
IntervalArray([(0, 1], (1, 2]],
              closed='right',
              dtype='interval[int64]')

We should convert that to the default EA repr.

[TomAugspurger]

FYI, there are some doctests that are shared between IntervalArray and IntervalIndex.