Rust: Remove excess 'cached' annotation.

Author: geoffw0

rust/ql/lib/codeql/rust/elements/internal/VariableImpl.qll

@@ -128,7 +128,6 @@ module Impl {
     Name getName() { variableDecl(definingNode, result, text) }
 
     /** Gets the block that encloses this variable, if any. */
-    cached
     BlockExpr getEnclosingBlock() { result = definingNode.getEnclosingBlock() }
 
     /** Gets the `self` parameter that declares this variable, if any. */