Revert "ULPError: avoid unnecessary conversion to BigFloat"

This reverts commit 33eca5f.

Author: nsajko

test/testhelpers/ULPError.jl

@@ -34,7 +34,7 @@ module ULPError
         ulp_error(acc, app)
     end
     function ulp_error(func::Func, x::AbstractFloat) where {Func}
-        ulp_error(func, func, x)
+        ulp_error(func ∘ BigFloat, func, x)
     end
     function ulp_error_maximum(func::Func, iterator) where {Func}
         function f(x::AbstractFloat)