Remove miri submodule

Author: oli-obk

.gitmodules

@@ -13,9 +13,6 @@
 [submodule "src/doc/book"]
 	path = src/doc/book
 	url = https://github.com/rust-lang/book.git
-[submodule "src/tools/miri"]
-	path = src/tools/miri
-	url = https://github.com/rust-lang/miri.git
 [submodule "src/doc/rust-by-example"]
 	path = src/doc/rust-by-example
 	url = https://github.com/rust-lang/rust-by-example.git