This is because of the System Integrity Protection (SIP).
You can disable it (not recommended) and remove the kext manually.
(from https://www.imore.com/el-capitan-system-integrity-protection-helps-keep-malware-away)
- Click the menu. Select Restart...
- Hold down command-R to boot into the Recovery System.
- Click the Utilities menu and select Terminal.
- Type
csrutil disable and press return.
- Close the Terminal app. Click the menu and select Restart....
If you decide later you want to re-engage SIP (and I earnestly hope that you do), repeat these steps, use csrutil enable instead.
