krb5: Remove recipe

We pick it up from meta-oe now.
flex: Append to 2.5.37
contents-runtime: Add libxml2
contents-devel: Add libxml2-dev
contents-runtime: Add libxslt
contents-devel: Add libxslt-dev
mauidistro.conf: Force llvm 3.1

We are now using meta-oe master and it has updated llvm.
However there are issues with mesa which prevents llvmpipe from working
due to some nasty asserts.
contents: Change libicule50 to libicule51

Poky now has icu 51.2.