Remove handling of impossible case from SA1006

The hash token identifies a preprocessor directive, so it's not possible to
have it be missing and also end up treating code like a preprocessor
directive.

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers/SpacingRules/SA1006PreprocessorKeywordsMustNotBePrecededBySpace.cs

@@ -76,11 +76,6 @@ private static void HandleSyntaxTree(SyntaxTreeAnalysisContext context)
 
         private static void HandleHashToken(SyntaxTreeAnalysisContext context, SyntaxToken token)
         {
-            if (token.IsMissing)
-            {
-                return;
-            }
-
             if (!token.HasTrailingTrivia || token.TrailingTrivia.Any(SyntaxKind.EndOfLineTrivia))
             {
                 return;