Fix: F999 dictionary key '2000q4' repeated with different values
Removal of duplicate line to fix lint error

```
pandas/tseries/tests/test_tslib.py:685:18: F999 dictionary key '2000q4' repeated with different values
pandas/tseries/tests/test_tslib.py:690:18: F999 dictionary key '2000q4' repeated with different values
```

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14198?src=pr) is 85.24% (diff: 100%)

> Merging [#14198](https://codecov.io/gh/pydata/pandas/pull/14198?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will not change coverage

``` diff
@@             master     #14198   diff @@
==========================================
  Files           140        140          
  Lines         50556      50556          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          43095      43095          
  Misses         7461       7461          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [289cd6d...82459ba](https://codecov.io/gh/pydata/pandas/compare/289cd6d0df66b812921ff4c5cbade937b875406d...82459ba45a37dedbbe47b93c714a698476f01628?src=pr)
 this is not a duplicate (it's lowercase)
otherwise the linter would have picked this up before
 @jreback  Have a look: https://github.com/pydata/pandas/blob/master/pandas/tseries/tests/test_tslib.py

line 685 vs line 690:
'2000q4': datetime.datetime(2000, 10, 1),
'2000q4': datetime.datetime(2000, 10, 1),

exactly the same. Line 681 is a different case: 

'2000Q4': datetime.datetime(2000, 10, 1),

Lint must have got more stick with repeated keys.
 hmm now it's failing 

https://travis-ci.org/pydata/pandas/jobs/158971225
