[KYUUBI #5908] [DOCS] Remove workaround for malformed table

# 🔍 Description
## Issue References 🔗

The `custom.css` was used to address the `sphinx-book-theme` bugs which generated malformed tables, see #1889 #2764 for details.

With the recent upgrading of `sphinx-book-theme 1.1.0`, it's unnecessary.

## Describe Your Solution 🔧

Remove useless `custom.css`

## Types of changes 🔖

- [ ] Bugfix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)

## Test Plan 🧪

#### Behavior Without This Pull Request ⚰️

<img width="1376" alt="image" src="https://github.com/apache/kyuubi/assets/26535726/1ef116f8-6be1-49ee-8f6e-3b844eae284a">

#### Behavior With This Pull Request 🎉

<img width="1376" alt="image" src="https://github.com/apache/kyuubi/assets/26535726/b12e461b-6294-4a4e-b034-fbd093b10ca4">

#### Related Unit Tests

---

# Checklists
## 📝 Author Self Checklist

- [ ] My code follows the [style guidelines](https://kyuubi.readthedocs.io/en/master/contributing/code/style.html) of this project
- [x] I have performed a self-review
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my feature works
- [ ] New and existing unit tests pass locally with my changes
- [x] This patch was not authored or co-authored using [Generative Tooling](https://www.apache.org/legal/generative-tooling.html)

## 📝 Committer Pre-Merge Checklist

- [ ] Pull request title is okay.
- [ ] No license issues.
- [ ] Milestone correctly set?
- [ ] Test coverage is ok
- [ ] Assignees are selected.
- [ ] Minimum number of approvals
- [ ] No changes are requested

**Be nice. Be informative.**

Closes #5908 from pan3793/remove-custom-css.

Closes #5908

a958b774c [Cheng Pan] nit
a3f592645 [Cheng Pan] [DOCS] Remove workaround for malformed table

Authored-by: Cheng Pan <chengpan@apache.org>
Signed-off-by: liangbowen <liangbowen@gf.com.cn>

docs/_static/css/custom.css

@@ -1,47 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-table.docutils {
-    width: 100%;
-    margin-top: 10px;
-    margin-bottom: 10px;
-    border: 0;
-    border-collapse: collapse;
-    table-layout: auto;
-}
-table.docutils th {
-    padding: 1px 8px 1px 5px;
-    border-top: 1px;
-    border-left: 1px;
-    border-right: 1px;
-    border-bottom: 1px solid #aaa;
-}
-table.docutils td {
-    word-break: break-word;
-    min-width: 10%;
-}
-table.docutils tr:hover {
-    background: #efefef;
-}
-table.docutils tbody tr:nth-child(2n) {
-    background: #9EBCE21E;
-}
-table.docutils td:nth-child(1) {
-    width: 25%;
-    word-break: break-all;
-    font-weight: 500;
-}

docs/conf.py

@@ -126,8 +126,7 @@ pygments_style = 'sphinx'
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
-html_css_files = ["css/custom.css"]
+html_static_path = []
 htmlhelp_basename = 'Recommonmarkdoc'
 
 github_doc_root = 'https://github.com/apache/kyuubi/tree/master/docs/'