This makes it consistent with Dolphin which will run scripts only if one is selected. If multiple are selected, they are opened in their preferred associated application (e.g. Kate) instead.

I also removed the restriction on opening folders when only one item is selected.

CCBUG: 375793

• Selected a script, hit return, got execution prompt (cf. D4367)
• Selected two scripts, hit return, both of them were opened in Kate
• Selected a folder, hit return, Dolphin opened it
• Selected multiple folders, nothing happened
• Selected multiple files and folders, only the files were opened in their associated application