The line of code you show should not be generating the compile warning in an Dashboard Extender rules file. Recompile the particular logic file and pay attention to the line of code it references having the issue. the compiler tells you very clearly the line of code and function that is the issue.
When moving to 8.0 or higher, a small but growing number of BRApi functions have been changed to require an additional pass-in parameter to specify the Workspace. When you click on the function on the line of code that is actually generating the compile warning, you should see there is an additional variant of the BRApi function that allows you to pass-in the WorkspaceId. Additionally, there just so happens to be a brand new 8.0 BRApi function that will return the WorkspaaceId. As such, most of the compile warnings for deprecating functions can be resolved in minutes. Even without fixing the deprecation function warnings, the code will *usually* continue to run without changes, so long as the Dashboard object you are after remains in the Default workspace, which buys you some time to resolve each warning. But, depending on your specific code, who knows. I think the functions that were depreciated in 8.0 are still supported in 9.0 - but don't quote me on that, as I resolved my codebase some time ago. In any event, you clearly need to fix the functions in a timely manner, as they are not going to remain forever. If/when you start using workspaces as they are intended, then you will need to pay a little more attention to the WorkspaceId you pass-in to these updated functions.
There have been a couple other BRApi function that have been marked as going away pertaining to passing/storing of passwords.