Looping through every subsequent paragraph is a very slow way to go about this. I would use a Find function which is way faster but has the drawback of not working with long paragraphs (I think the limit is 255 characters). I suspect the subtitles are generally short so this might not be a problem for you.
Code:
Sub DeleteDuplicates()
Dim aRng As Range, aPara As Paragraph, sText As String
Set aPara = ActiveDocument.Paragraphs.First
Do While aPara.Range.End <> ActiveDocument.Range.End
If Len(aPara.Range.Text) > 1 Then
sText = aPara.Range.Text
Debug.Print sText
Set aRng = ActiveDocument.Range
aRng.Start = aPara.Range.End
With aRng.Find
.ClearFormatting
.Replacement.ClearFormatting
.Text = sText
.Replacement.Text = ""
.Forward = True
.Wrap = wdFindStop
.Format = False
.MatchCase = False
.MatchWholeWord = False
.MatchWildcards = False
.MatchSoundsLike = False
.MatchAllWordForms = False
.Execute Replace:=wdReplaceAll
End With
End If
Set aPara = aPara.Next
Loop
End Sub