Pandas won't drop index after rename using said index
So, there should probably be a 'drop' option as part of the rename function to drop said index if using it, but like the title says, if you rename using an index, you can't then use the drop function to drop said index (tested with xlsx and csv)

works for whatever index, 1, 2, 3, etc.
[testfile.xlsx](https://github.com/pandas-dev/pandas/files/4532369/testfile.xlsx)


```
    dataframe = pandas.read_excel(ENVT_SETTINGS['working_dir'] + 'testfile.xlsx', engine='openpyxl', header=None)
    
    print(dataframe.head(5))
    dataframe.rename(columns = dataframe.iloc[0], inplace = True)
    print(dataframe.head(5))
    dataframe.drop(dataframe.index[0])
    print(dataframe.head(5))
```
interestingly, you CAN drop it if you then recreate the dataframe like
`    dataframe = dataframe[1:]`
to literally cut out that row from the dataset, but otherwise, it won't go away.
[testfile.xlsx](https://github.com/pandas-dev/pandas/files/4532379/testfile.xlsx)
[testresult.xlsx](https://github.com/pandas-dev/pandas/files/4532380/testresult.xlsx)

