remove knowhere submodule

Former-commit-id: 23258a4051947552fca3ffc673b408ab92792eac

.gitmodules

-[submodule "cpp/thirdparty/knowhere"]
-	path = cpp/thirdparty/knowhere
-	url = git@192.168.1.105:megasearch/knowhere.git
-	branch = branch-0.4.0