BUG: TimedeltaIndex division not supported
#### Code Sample, a copy-pastable example if possible

```python
>>> t1 = pd.timedelta_range('0 days', '4 days', periods=5)
>>> t2 = pd.timedelta_range('0 days', '4 days', periods=5)

>>> t1 / t2
Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'TimedeltaIndex' and 'TimedeltaIndex'
```
#### Problem description
At least in Pandas 0.20.3 it was possible to divide TimedeltaIndex instances, but in the current stable version I get TypeError. 
#### Expected Output

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.7.final.0
python-bits: 64
OS: Darwin
OS-release: 18.0.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8
pandas: 0.23.4
pytest: 3.3.1
pip: 18.1
setuptools: 40.6.2
Cython: None
numpy: 1.15.0
scipy: None
pyarrow: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.7.5
pytz: 2018.7
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None


</details>
