ZWSP is shown as ​

**Describe the bug**

Since https://github.com/matrix-org/matrix-appservice-irc/pull/1366 matrix-appservice-irc doesn't strip ZWSPs and thus Matrix users through IRC bridged relaybots may look weird.

**To Reproduce**
Steps to reproduce the behavior:
1. Go to `#test:matrix.org` and https://web.libera.chat/#matrix-test
2. Copy-Paste `2021-162 17:24:12 EEST <@T4> M​ikaela/Etro: meow-meow choco-chow` (or other ZWSP) to the second link
3. Look at `#test:matrix.org` on Element iOS
4. See a mysterious `​` instead of nothing special in the message.

**Expected behavior**

Not seeing ZWSP as it's supposed to be invisible.

**Screenshots**

The sample message in both Element iOS and Element Web in that order.

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**Smartphone (please complete the following information):**
- Device: iPhone SE2020
- OS: iOS 14.6
- Browser: stock Safari
- Version: iOS 14.6?

**Additional context**

Using ZWSP is common behaviour in IRC relaybots to avoid self-pinging when on multiple sides of the relay.