Remove deprecated information about performances:
* It is better if we leave third parties to do "independent" benchmark.
* We compare Clang (version unspecified) with gcc 4.0 or 4.2.
* The graphs have not been updated for a while.
* Clang is well known now. I don't think we still need to explain why
Clang is great.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207358 91177308-0d34-0410-b5e6-96231b3b80d8