Resolve ESlint warnings

[gareth]

The repo is configured with ESlint rules but they currently generate warnings:

$ npm exec eslint .

./Archipelago/ArchipelagoInterface.js
  1:72  warning  'ConnectionStatus' is assigned a value but never used  no-unused-vars
  2:9   warning  'User' is assigned a value but never used              no-unused-vars

./bot.js
  8:1  warning  'process' is not defined  no-undef
  9:1  warning  'process' is not defined  no-undef

./channelDeletedListeners/apInterfaceCloser.js
  1:9   warning  'Client' is assigned a value but never used        no-unused-vars
  1:17  warning  'GuildChannel' is assigned a value but never used  no-unused-vars

./scripts/registerSlashCommands.js
   9:55  warning  '__filename' is not defined  no-undef
  14:44  warning  '__filename' is not defined  no-undef

✖ 8 problems (0 errors, 8 warnings)

Although they're only warnings, I figure the config is there for a reason, so this PR resolves the issues.

Half of the issues were because ESlint was configured for browser environments, and ArchipelaBot isn't run in-browser, so this updates the config to correctly check in a node context.