Temporarily remove the 5.1.18 release note

So that it doesn't show up on the prerelease

editions/prerelease/tiddlers/Release 5.1.18.tid

@@ -1,43 +0,0 @@
-caption: 5.1.18
-created: 20180502140428597
-modified: 20180502140428597
-tags: ReleaseNotes
-title: Release 5.1.18
-type: text/vnd.tiddlywiki
-
-//[[See GitHub for detailed change history of this release|https://github.com/Jermolene/TiddlyWiki5/compare/v5.1.17...v5.1.18]]//
-
-!! New and Improved Plugins
-
-* 
-
-!! Translation Improvements
-
-New and improved translations:
-
-* 
-
-!! Usability Improvements
-
-* 
-
-!! Hackability Improvements
-
-* 
-
-!! Bug Fixes
-
-* 
-
-!! Developer Bug Fixes and Improvements
-
-* 
-
-
-! Contributors
-
-[[@Jermolene|https://github.com/Jermolene]] would like to thank the contributors to this release who have generously given their time to help improve TiddlyWiki:
-
-* [[@example|https://github.com/example]]
-
-