Rust: Remove the now empty files.

Author: geoffw0

rust/ql/lib/codeql/rust/Frameworks.qll

@@ -2,7 +2,5 @@
  * This file imports all models of frameworks and libraries.
  */
 
-private import codeql.rust.frameworks.Reqwest
 private import codeql.rust.frameworks.rustcrypto.RustCrypto
-private import codeql.rust.frameworks.stdlib.Env
 private import codeql.rust.frameworks.Sqlx