[clang] [flang] [flang][driver] Rename `flang-new` as `flang` (PR #74377)

[Andrzej Warzyński via cfe-commits]

================
@@ -15,17 +15,13 @@ local:
 ```
 
 There are two main drivers in Flang:
----------------
banach-space wrote:

Good point 👍🏻 

https://github.com/llvm/llvm-project/pull/74377