Issue 7133 - Avoid duplicating filters in the test subscription

For reference, here's what the generated subscription looks like:

[Adblock Plus 2.0]

! exceptions/elemhide
localhost##.testcase-ex-elemhide
||localhost:5000/testcasefiles/elemhide/image.jpg
@@localhost:5000/en/exceptions/elemhide^$elemhide

! exceptions/popup
||localhost:5000/en/exceptions/popup^$popup
@@||localhost:5000/en/exceptions/popup^$popup
||localhost:5000/en/popuptarget^$popup
@@||localhost:5000/en/filters/popup-exception^$popup

! exceptions/subdocument
||localhost:5000/testcasefiles/subdocumentexception/*
@@localhost:5000/testcasefiles/subdocumentexception/$subdocument

! exceptions/document
localhost##.testcase-ex-document
||localhost:5000/testcasefiles/document/*
@@localhost:5000/en/exceptions/document^$document

! exceptions/xmlhttprequest
||localhost:5000/testcasefiles/xmlhttprequestexception/*
@@localhost:5000/testcasefiles/xmlhttprequestexception/$xmlhttprequest

! exceptions/element-hiding
localhost##.testcase-ehe
localhost#@#.testcase-ehe

! exceptions/script
||localhost:5000/testcasefiles/scriptexception/*
@@localhost:5000/testcasefiles/scriptexception/$script

! exceptions/stylesheet
||localhost:5000/testcasefiles/stylesheetexception/*
@@localhost:5000/testcasefiles/stylesheetexception/$stylesheet

! exceptions/image
||localhost:5000/testcasefiles/imageexception/*
@@localhost:5000/testcasefiles/imageexception/$image

! filters/object-subrequest
localhost:5000/testcasefiles/objectsubrequest/$object-subrequest

! filters/blocking
||localhost:5000/testcasefiles/blocking/addresscomplete/image.jpg
/testcasefiles/blocking/addresspart/abptestcasepath/
||localhost:5000/testcasefiles/blocking/wildcard/*/image.jpg

! filters/popup
||localhost:5000/en/popuptarget^$popup
||localhost:5000/en/popuptarget^$popup

! filters/object
localhost:5000/testcasefiles/object/$object

! filters/ping
localhost:5000/*^$ping
localhost:5000/*^$ping

! filters/subdocument
localhost:5000/testcasefiles/subdocument/$subdocument

! filters/webrtc
$webrtc,domain=localhost

! filters/xmlhttprequest
localhost:5000/testcasefiles/xmlhttprequest/$xmlhttprequest

! filters/element-hiding-emulation
localhost#?#div:-abp-properties(width: 213px)
localhost#?#div:-abp-has(>div>img.testcase-es-has)
localhost#?#span:-abp-contains(ESContainsTarget)
localhost#?#div:-abp-has(> div:-abp-properties(width: 214px))
localhost#?#div:-abp-properties(WiDtH: 215px)
localhost#?#div:-abp-properties(cursor:*)
localhost#?#div:-abp-properties(/width: 12[1-5]px;/)
localhost#?#div > div:-abp-contains(/ESContainsRegEx\d/)

! filters/element-hiding
localhost###testcase-eh-id
localhost##.testcase-eh-class
localhost##.testcase-container > .testcase-eh-descendant
localhost##.testcase-eh-sibling + .testcase-eh-sibling-target
localhost##table[height="100"][width="100"]
localhost##a[href="http://testcase-attribute.com/"]
localhost##div[style="width:199px;height:51px;"]
localhost##a[href^="http://testcase-attributestartswith.com/"]
localhost##div[style^="width:201px;height:51px;"]
localhost##div[style$="width:202px;height:51px;"]
localhost##div[style*="width:203px;height:51px;"]

! filters/script
localhost:5000/testcasefiles/script/$script

! filters/websocket
$websocket,domain=localhost

! filters/stylesheet
localhost:5000/testcasefiles/stylesheet/$stylesheet

! filters/match-case
/testcasefiles/matchcase/*/abc.jpg$match-case

! filters/image
localhost:5000/testcasefiles/image/$image