Improve the performance of instantiating a Series object with dictionary data and a datetimeindex
The current code path always results in an exception on:
https://github.com/pandas-dev/pandas/blob/3ac41ab2d7ae446fa04f47ec911003cd722dbd65/pandas/core/series.py#L191

which is then caught.  Only a slight performance advantage is seen but hopefully the code change  makes it less confusing for newcomers like me.

#### Code Sample, a copy-pastable example if possible

```python
dr = pd.date_range(
            start=datetime(2015, 10, 26),
            end=datetime(2016, 1, 1),
            freq='10s'
        )
data = {d: v for d, v in zip(dr, range(len(dr)))}
s = Series(data=data, index=dr)
```
#### Problem description

The current code path always results in an exception on:
https://github.com/pandas-dev/pandas/blob/3ac41ab2d7ae446fa04f47ec911003cd722dbd65/pandas/core/series.py#L191

which is then caught.  Only a slight performance advantage is seen but hopefully the code change  makes it less confusing for newcomers like me.

ASV output of new benchmark
 Running 2 total benchmarks (2 commits * 1 environments * 1 benchmarks)
[  0.00%] · For pandas commit hash 5f05fdcf:
[  0.00%] ·· Building for conda-py2.7-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt.................................
[  0.00%] ·· Benchmarking conda-py2.7-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt
[ 50.00%] ··· Running ...x.time_series_constructor_no_data_datetime_index      3.26s
[ 50.00%] · For pandas commit hash 3ba2cff9:
[ 50.00%] ·· Building for conda-py2.7-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt...
[ 50.00%] ·· Benchmarking conda-py2.7-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt
[100.00%] ··· Running ...x.time_series_constructor_no_data_datetime_index      3.77s    before     after       ratio
  [3ba2cff9] [5f05fdcf]
-     3.77s      3.26s      0.87  series_methods.series_constructor_dict_data_datetime_index.time_series_constructor_no_data_datetime_index