delete libpaw (deepmodeling#7273)

Co-authored-by: abacus_fixer <mohanchen@pku.eud.cn>

Author: mohanchen

.gitmodules

@@ -1,4 +0,0 @@
-[submodule "deps/libpaw_interface"]
-	path = deps/libpaw_interface
-	url = https://github.com/wenfei-li/libpaw_interface
-	branch = master