docs: remove ToC from CONTRIBUTING.md

In SeleniumHQ#443 there is complains that the ToC makes the page harder to read.
I tend to agree as on a small screen I can't see anything but the ToC.

CONTRIBUTING.md

@@ -3,24 +3,6 @@
 The Selenium project welcomes contributions from everyone. There are a
 number of ways you can help:
 
-## Table of Contents
-- [Contributing to Selenium](#contributing-to-selenium)
-  - [Issue Contributions](#issue-contributions)
-  - [Documentation Contributions](#documentation-contributions)
-  - [Code Contributions](#code-contributions)
-    - [Step 1: Fork](#step-1-fork)
-      - [Dependencies](#dependencies)
-      - [License Headers](#license-headers)
-    - [Step 2: Branch](#step-2-branch)
-    - [Step 3: Commit](#step-3-commit)
-    - [Step 4: Rebase](#step-4-rebase)
-    - [Step 5: Test](#step-5-test)
-    - [Step 6: Sign the CLA](#step-6-sign-the-cla)
-    - [Step 7: Push](#step-7-push)
-    - [Step 8: Integration](#step-8-integration)
-  - [Stages of an Issue or PR](#stages-of-an-issue-or-pr)
-  - [Communication](#communication)
-
 ## Issue Contributions
 
 When opening new issues or commenting on existing issues on this