Remove WEBKIT_VERSION_MIN_REQUIRED and config.h.

WebKit style guide (https://www.webkit.org/coding/coding-style.html)
explicitly states:

> All implementation files must #include "config.h" first.
> Header files should never include "config.h".

Also, it isn't currently being used.

TBR=reed@google.com
This just removes unused bits.

Review URL: https://codereview.chromium.org/1256133004
1 file changed