remove normative reference to HTML5

The current WD of WOFF File Format 1.0 [1] has an erroneous reference to
HTML5, which is not referred to in the specification; therefore, it should
be removed. One must not have a normative reference unless it is used
normatively.

Regards,
Glenn Adams

[1] http://www.w3.org/TR/2010/WD-WOFF-20101116/