remove tuirs_popup_placeholder example

Cargo.toml

@@ -95,10 +95,6 @@ required-features = ["tuirs-crossterm"]
 name = "tuirs_editor"
 required-features = ["tuirs-crossterm", "search"]
 
-[[example]]
-name = "tuirs_popup_placeholder"
-required-features = ["tuirs-crossterm"]
-
 [[example]]
 name = "tuirs_termion"
 required-features = ["tuirs-termion"]