You could write an Add-In to do this, but for quick and easy I did it with this Macro and added a button to my Toolbar to run it:
Imports EnvDTE
Public Module Module1
Sub RemoveSmartQuotes()
Dim sFind() As String = New String() {Chr(145), Chr(146), Chr(147), Chr(148)}
Dim sReplace() As String = New String() {Chr(39), Chr(39), Chr(34), Chr(34)}
For i As Integer = 0 To sFind.Length - 1
DTE.Find.Action = vsFindAction.vsFindActionReplaceAll
DTE.Find.FindWhat = sFind(i)
DTE.Find.ReplaceWith = sReplace(i)
DTE.Find.Target = vsFindTarget.vsFindTargetCurrentDocument
DTE.Find.MatchCase = False
DTE.Find.MatchWholeWord = False
DTE.Find.MatchInHiddenText = True
DTE.Find.PatternSyntax = vsFindPatternSyntax.vsFindPatternSyntaxLiteral
DTE.Find.KeepModifiedDocumentsOpen = False
DTE.Find.FilesOfType = ""
DTE.Find.ResultsLocation = vsFindResultsLocation.vsFindResultsNone
DTE.Find.Execute()
Next i
End Sub
End Module