fix(Util): cleanContent should remove mentions after formatting mentions

[NotSugden]

Please describe the changes this PR makes and why it should be merged:
Util.cleanContent currently removes possible everyone mentions then formats mentions, this could result in that being bypassed if a user had the username 'everyone' or a role had the name 'everyone'
Status

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

Semantic versioning classification:

• This PR changes the library's interface (methods or parameters added)
  • This PR includes breaking changes (methods removed or renamed, parameters moved or removed)
• This PR only includes non-code changes, like changes to documentation, README, etc.