The quick and dirty way is to repeat the relevant code. I'm sure if I thought hard enough it could be made more elegant but I haven't the time today
Code:
Sub RemoveJoin()
Dim oRng As Range, iType As Integer
Set oRng = ActiveDocument.Range
With oRng.Find
.ClearFormatting
.Text = "joined the meeting^p"
While .Execute
oRng.Paragraphs(1).Range.Delete
Wend
End With
Set oRng = ActiveDocument.Range
With oRng.Find
.ClearFormatting
.Text = "left the meeting^p"
While .Execute
oRng.Paragraphs(1).Range.Delete
Wend
End With
End Sub