PERF: Use Categorical.equals in CategoricalIndex.equals
Avoids a materialization of the full array.

```python
import pandas as pd
import numpy as np
import string


a = pd.CategoricalIndex(np.random.choice(list(string.ascii_letters[:10]), 100_000))
b = a.copy()
c = pd.CategoricalIndex(np.random.choice(list(string.ascii_letters[:10]), 100_000))

print("eq-index")
%timeit a.equals(b)

print("ne-index")
%timeit a.equals(c)
```


timings

case      | master | pr
--------- | ------- | --
eq-index  | 3.35 ms | 420 µs
ne-index  | 1.29 ms | 451 µs

Hello @TomAugspurger! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/indexes/category.py`](https://github.com/TomAugspurger/pandas/blob/09e07d2ae26008d203bc84e4721fa83ff484e662/pandas/core/indexes/category.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24023?src=pr&el=h1) Report
> Merging [#24023](https://codecov.io/gh/pandas-dev/pandas/pull/24023?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/dc8d35aa53d496b651f5e1ab4cb2604e9f7236c7?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24023/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24023?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24023      +/-   ##
==========================================
+ Coverage   92.31%   92.31%   +<.01%     
==========================================
  Files         161      161              
  Lines       51549    51551       +2     
==========================================
+ Hits        47586    47588       +2     
  Misses       3963     3963
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.71% <100%> (ø)` | :arrow_up: |
| #single | `42.45% <100%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24023?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/category.py](https://codecov.io/gh/pandas-dev/pandas/pull/24023/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9jYXRlZ29yeS5weQ==) | `97.88% <100%> (+0.01%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24023?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24023?src=pr&el=footer). Last update [dc8d35a...f35e8dd](https://codecov.io/gh/pandas-dev/pandas/pull/24023?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!