BUG: Categorical order lost after call to remove_categories

[jinlow]

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Reproducible Example

import pandas as pd

c = pd.Series(
    [
        "a",
        "b",
        "c",
        "d",
        "d",
        "a",
    ],
    dtype="category",
).cat.reorder_categories(["d", "c", "b", "a"], ordered=True)
print(c.cat.categories) # Index(['d', 'c', 'b', 'a'], dtype='object')
c = c.cat.remove_categories("c")
print(c.cat.categories) # Index(['a', 'b', 'd'], dtype='object')

Issue Description

When remove_categories is called on an ordered categorical series, the returned series loses it's order.

Expected Behavior

In the example, I would expect the new order to be to be ['d', 'b', 'a'] after "c" is removed, rather than ['a', 'b', 'd'].

Installed Versions

INSTALLED VERSIONS

commit : 0f43794
python : 3.10.4.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.22621
machine : AMD64
processor : Intel64 Family 6 Model 140 Stepping 1, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United States.1252

pandas : 2.0.3
numpy : 1.25.0
pytz : 2023.3
dateutil : 2.8.2
setuptools : 68.0.0
pip : 22.0.4
Cython : None
pytest : 7.4.0
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : 3.1.2
lxml.etree : 4.9.2
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.14.0
pandas_datareader: None
bs4 : 4.12.2
bottleneck : None
brotli : None
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : 3.7.1
numba : None
numexpr : None
odfpy : None
openpyxl : 3.1.2
pandas_gbq : None
pyarrow : 12.0.1
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.11.0
snappy : None
sqlalchemy : None
tables : None
tabulate : 0.9.0
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.3
qtpy : None
pyqt5 : None

[phofl]

Thanks! This looks odd, investigations welcome

[paulreece]

I have found the root of this issue and will submit a PR later this evening.

[paulreece]

Here is a link to my PR with the fix, and detailing the logic behind it. #54027