Update library/core/src/intrinsics/mir.rs

Co-authored-by: Rémy Rakic <remy.rakic+github@gmail.com>

Author: cjgillot

library/core/src/intrinsics/mir.rs

@@ -251,7 +251,7 @@
 //!
 //! #### Debuginfo
 //!
-//!  - A a debuginfo name can be given to a local using `debug my_name => contents;`.
+//!  - A debuginfo name can be given to a local using `debug my_name => contents;`.
 //!    For `contents`, we use the same syntax as operands, to support both places and constants.
 //!