Disabled UCSC DAS Data Provider by default and tested a few functionalities to make sure disabling DAS isn't causing any issues. Everything is working as usual. Updated code is at the branch: https://bitbucket.org/jaya-sravani/integrated-genome-browser/branch/IGBF-3655. Below are screenshots of few tested scenarios:
Loading of human genome with updated UCSC REST code and after disabling DAS (took around 3-4 secs to load):

External View loaded correctly without any issue:

Redirect to UCSC genome browser also worked fine:

Please review and let me know if there are any issues.
To Test:

1. Make sure your igb preferences are reset before running the above branch installer jar or building the application from the above branch.
2. Now, after IGB is started, click on the configure button in the available data panel and check whether UCSC DAS is disabled by default.
3. Also, select any genome and check whether the DAS tracks are not being loaded.

Tested Sravani's branch on Mac.

DAS was disabled by default. External View and the View Region in UCSC Browser menu option worked correctly. I also tested the trackhubs page (https://www.bioviz.org/public-trackhubs.html) as there was an issue (IGBF-3053) that describes needing DAS enabled by default. The UCSC REST data provider works to provide the same functionality that DAS had previously provided, and the trackhubs were able to be added and the genomes viewed. There is a separate issue (IGBF-2862) that should be addressed, but is not directly related to this ticket.

Ready for pull request.

Raised pull request: https://bitbucket.org/lorainelab/integrated-genome-browser/pull-requests/1009. Please review and let me know if there are any issues.

PR is merged. Installers are build and deployed to bioviz.org "early access" section for testing.