FindGit: remove EasyGit

Blame shows EasyGit was part of initial FindGit 11 years ago.
I can hardly find Easy Git as a package. Given that Git is vital
for many complex CMake projects, it seems good to ensure CMake
FindGit is finding a Git program likely to work.

Crucial CMake modules like FetchContent also use FindGit, emphasizing
the importance of having a Git executable with proper functionality.