Fix ESLint Errors in Several Files

[ansulagrawal]

In the react-big-schedule project, several ESLint errors need to be addressed to ensure consistent code quality and avoid potential bugs. The affected files are:

1. react-big-schedule/src/components/SchedulerData.js
2. react-big-schedule/src/components/DnDSource.js
3. react-big-schedule/src/components/DnDContext.js

Each file needs to be reviewed and updated to comply with the project's ESLint rules. Please note the importance of not disabling the ESLint rules globally or within the files, as this might mask other potential issues.

Please use the npm run lint command after making the changes to ensure that all ESLint errors have been successfully fixed.

Thanks in advance for your attention to this issue.