Web IDE: Remove properties `branchId`, `projectId` from the file object

Web IDE now only supports opening a single project and a single branch at a time, so we can get rid of these properties on the file object.

Proposal

• projectId -> This property is unnecessary on the file object since at a time only one project and branch can be open in the Web IDE. The usage can be replaced with currentProjectId in state.
• branchId -> Same as above. Can be replaced with currentBranchId in state.