remove gitignore entries for cargo stuffs

Any code by Rust language might not be maintained in the repository.

Signed-off-by: Takashi Sakamoto <[email protected]>

.gitignore

@@ -1,10 +0,0 @@
-# Generated by Cargo
-# will have compiled files and executables
-/target/
-
-# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
-# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
-Cargo.lock
-
-# These are backup files generated by rustfmt
-**/*.rs.bk