Drop redundant attributes in hardcoded html

Follows-up 97caae596d5493 which makes HTML5 the default
and removes support for XHTML 1.0 and HTML < 5.

* <script type>
* <style type>
* <html xmlns>
* Quick-closing slash in non-XML HTML5 documents

Change-Id: I71855fa8d4095a5a448ebdc3dc36506ddab6f70c
Deprecate $wgJsMimeType

It hasn't been used for its documented purpose for a while.
In fact the one significant thing it can cause wasn't even
documented. If set to anything other than "text/javascript"
it will cause action=raw to no longer respond to
ctype=text/javascript requests (such as done by wikibits'
importScript function).

Follows-up 97caae596d5493.

Change-Id: Ib04ff5b21eb0ae172b94e31bc0dc16c9649e1864