Flexdashboard apps removal and consolidation

[MadhulikaTanuboddi]

After a discussion with Barret and Carson, we agreed to remove the following flexdashboard apps

201-flexdashboard-sales-report
202-flexdashboard-kmeans
203-flexdashboard-biclustering

These apps are a good demo apps but does not serve the purpose of testing and are not a good fit to review/catch any bugs in shinycoreci-apps. App200-flexdashboard-render-text is a good testing app that tests shiny inputs and outputs and dynamicn rendering of the text (months in this case).

Also, above apps consistently fail with one or the other reason. More context at https://trello.com/c/5XEbfNK4/2295-pkg-shinycoreci-apps-fix-discuss-flexdashboard-issues

We also decided we could move certain key shiny input and output functions and usage from all of the above apps to 200-flexdashboard-render-text. @schloerke will be taking care of this.

In the future, we should add a new app that tests bslib theming with flexdashboard cc: @cpsievert See #130