Remove single file example

The example will be moved to the gallery.

inst/examples/12_singlefile/DESCRIPTION

@@ -1,7 +0,0 @@
-Title: Single-file shiny app
-Author: RStudio, Inc.
-AuthorUrl: http://www.rstudio.com/
-License: MIT
-DisplayMode: Showcase
-Tags: getting-started
-Type: Shiny

inst/examples/12_singlefile/app.R

@@ -1,20 +0,0 @@
-# Global variables can go here
-n <- 200
-
-
-# Define the UI
-ui <- bootstrapPage(
-  numericInput('n', 'Number of obs', n),
-  plotOutput('plot')
-)
-
-
-# Define the server code
-server <- function(input, output) {
-  output$plot <- renderPlot({
-    hist(runif(input$n))
-  })
-}
-
-# Return a Shiny app object
-shinyApp(ui = ui, server = server)