Fix ESlint errors for web-pubsub-express package

[ramya-rao-a]

We have the linter enabled for the @azure/web-pubsub-express package, and have a quite a few linter errors to fix

This issue is to ensure that we fix the these errors so that we future regressions can be found in CI. Following are the steps to run ESLint and reproduce this issue.

Set up your dev environment if not already done so as mentioned here

• Go to <repo root>/sdk/web-pubsub/web-pubsub-express in your terminal
• Run rushx lint. This will generate an html report with name ending with lintReport.html in the same folder
• Fix one or more of the linter errors in the html report, and send a PR!

Once all linter errors are fixed, update the lint script in the package.json file to remove the below so that any new linter errors would fail the CI

-f html -o <package name>-lintReport.html || exit 0

[ramya-rao-a]

@vicancy In #17301, we have fixed quite a few of these errors that are straightforward and did not need any context on the source code. Please take a look at the rest of the linter errors and fix at them the earliest