Do not send the fragment part when requesting UrlPreview data

[bmarty]

• Send https://github.com/vector-im/element-android/pull/3448/files#diff-63b96f47c62869ba88e77317ff6a0b31483a6ebee57f5669c8be0c0eefce5c4aR19 in an unencrypted room.
• Observe that the request https://matrix-client.matrix.org/_matrix/media/r0/preview_url?url=https%3A%2F%2Fgh.neting.cc%2Fvector-im%2Felement-android%2Fpull%2F3448%2Ffiles%23diff-63b96f47c62869ba88e77317ff6a0b31483a6ebee57f5669c8be0c0eefce5c4aR19 is send to the server.

The fragment part #diff-63b96f47c62869ba88e77317ff6a0b31483a6ebee57f5669c8be0c0eefce5c4aR19 should not be send to the server.

But the fragment part should be restored when we render the URL preview in the timeline, because the link has definitely not the same value without the fragment part, and the user wants to see the same page when clicking on the preview and when clicking on the link from the message.