Remove extraneous text/vnd.tiddlywiki from system tiddlers in light of #2883

There’s no special reason for these tiddlers to be viewed wikified

core/acknowledgements.tid

@@ -1,5 +1,4 @@
 title: $:/Acknowledgements
-type: text/vnd.tiddlywiki
 
 TiddlyWiki incorporates code from these fine OpenSource projects:
 

core/language/en-GB/Modals/Download.tid

@@ -1,5 +1,4 @@
 title: $:/language/Modals/Download
-type: text/vnd.tiddlywiki
 subtitle: Download changes
 footer: <$button message="tm-close-tiddler">Close</$button>
 help: http://tiddlywiki.com/static/DownloadingChanges.html

core/language/en-GB/Modals/SaveInstructions.tid

@@ -1,5 +1,4 @@
 title: $:/language/Modals/SaveInstructions
-type: text/vnd.tiddlywiki
 subtitle: Save your work
 footer: <$button message="tm-close-tiddler">Close</$button>
 help: http://tiddlywiki.com/static/SavingChanges.html

core/templates/static.content.tid

@@ -1,5 +1,4 @@
 title: $:/core/templates/static.content
-type: text/vnd.tiddlywiki
 
 <!-- For Google, and people without JavaScript-->
 This [[TiddlyWiki|http://tiddlywiki.com]] contains the following tiddlers:

core/wiki/macros/timeline.tid

@@ -2,7 +2,6 @@ created: 20141212105914482
 modified: 20141212110330815
 tags: $:/tags/Macro
 title: $:/core/macros/timeline
-type: text/vnd.tiddlywiki
 
 \define timeline-title()
 <!-- Override this macro with a global macro 

core/wiki/title.tid

@@ -1,4 +1,3 @@
 title: $:/core/wiki/title
-type: text/vnd.tiddlywiki
 
 {{$:/SiteTitle}} --- {{$:/SiteSubtitle}}

editions/prerelease/tiddlers/system/DefaultTiddlers.tid

@@ -1,7 +1,6 @@
 created: 20131127215321439
 modified: 20140912135951542
 title: $:/DefaultTiddlers
-type: text/vnd.tiddlywiki
 
 [[TiddlyWiki Pre-release]]
 HelloThere

editions/prerelease/tiddlers/system/SiteTitle.tid

@@ -1,6 +1,5 @@
 created: 20131211131022562
 modified: 20131211131023829
 title: $:/SiteTitle
-type: text/vnd.tiddlywiki
 
 TiddlyWiki Pre-release

editions/tw5.com/tiddlers/system/static.content.tid

@@ -1,5 +1,4 @@
 title: $:/core/templates/static.content
-type: text/vnd.tiddlywiki
 hack-to-give-us-something-to-compare-against: yes
 
 \define tv-wikilink-template() http://tiddlywiki.com/static/$uri_doubleencoded$.html