[www] Remove implemented Open Project
"Open LLVM Projects" page is used by students willing to apply for Google
Summer of Code, this patch updates the page by removing the "Reimplement LLDB's
command-line commands using the public SB API" project implemented during GSoC 2018.
Subscribers: apolyakov, lldb-commits
Differential Revision: https://reviews.llvm.org/D57091