drop "Portable Toilets" preset

[tyrasd]

Fixes #1148 and in addition changes the following strings:

• rename generic amenity=toilets preset to "Toilets" (was: "Restroom"), as restroom is typically only used for rooms in a building, but the tag can also be used for outdoor toilets
• rename field for "toilets" tag to "Restroom" (for the opposite reason as above)
• move alias "Water Closet" to "Flush Toilets" preset

[github-actions[bot]]

:bento: You can preview the tagging presets of this pull request here.