Dropped columns still available for filtering
#### Code Sample
```python3
import pandas as pd
df = pd.DataFrame(data={'foo': [0, 1], 'bar': ["a", "b"]})
df.drop(columns=["bar"])[df["bar"] == "a"]
```

#### Problem description
The code sample above should result in an error like the following:

```
KeyError: 'bar'
```

However, it does not but instead works without error, as if the column "bar" would exist.

#### Output of ``pd.show_versions()``
```
INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.6.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.13.0-38-generic
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 0.25.3
numpy            : 1.17.4
pytz             : 2018.5
dateutil         : 2.8.0
pip              : 19.3.1
setuptools       : 41.6.0
Cython           : 0.29.6
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : 1.0.1
pymysql          : None
psycopg2         : 2.7.5 (dt dec pq3 ext lo64)
jinja2           : 2.10
IPython          : 7.5.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : 3.0.3
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : 1.3.1
sqlalchemy       : 1.2.10
tables           : None
xarray           : 0.14.1
xlrd             : 1.2.0
xlwt             : None
xlsxwriter       : None
```
