tests: Trim .nim files trailing whitespace

via OSX: find . -name '*.nim' -exec sed -i '' -E 's/[[:space:]]+$//' {} +

tests/trmacros/tcse.nim

@@ -6,7 +6,7 @@ template cse{f(a, a, x)}(a: expr{(nkDotExpr|call|nkBracketExpr)&noSideEffect},
                          f: expr, x: varargs[expr]): expr =
   let aa = a
   f(aa, aa, x)+4
-  
+
 var
   a: array[0..10, int]
   i = 3