Attribute "dir" is duplicated in the "built-in safe default configuration"

[evilpie]

We end up with a duplicate dir attribute in the built-in safe default configuration "attributes" list. This is caused by having both a MathML and HTML global dir attribute in safe-default-configuration.txt. (These attributes are both in the null namespace, so they are completely indistinguishable in context of the Sanitizer API)

[otherdaniel]

Agreed. It might be easiest to just check for duplicates in the script that generates it. That way, we can keep the source document readable.

[otherdaniel]

I forgot about #252 and that I need to manually re-run the build scripts in order to see their effect. Will add another PR. :/

Right now, dir is still in there twice, but re-running the script indeed fixes that.

[mozfreddyb]

thank you