remove .DS_Store which not related with source codes

[Ja-sonYun]

We don't need .DS_Store. Seems like .DS_Store already included in .gitignore, but still there. https://github.com/salesforce/CodeTF/blob/c79401732f4b2aafbe6abffaf3ddf362a5fad56e/.gitignore#L161

[salesforce-cla[bot]]

Thanks for the contribution! Before we can merge this, we need @Ja-sonYun to sign the Salesforce Inc. Contributor License Agreement.