[clang] Remove no-op -fexperimental-new-pass-manager/-fno-legacy-pass-manager flags

These have been no-op for a while and keeping them around may be confusing.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D136789

Author: aeubanks

clang/docs/ReleaseNotes.rst

@@ -158,6 +158,8 @@ code bases.
       }
     }
 
+  - The ``-fexperimental-new-pass-manager`` and ``-fno-legacy-pass-manager``
+    flags have been removed. These have been no-ops since 15.0.0.
 
 What's New in Clang |release|?
 ==============================

clang/include/clang/Driver/Options.td

@@ -2014,10 +2014,6 @@ def fglobal_isel : Flag<["-"], "fglobal-isel">, Group<f_clang_Group>,
   HelpText<"Enables the global instruction selector">;
 def fexperimental_isel : Flag<["-"], "fexperimental-isel">, Group<f_clang_Group>,
   Alias<fglobal_isel>;
-def fno_legacy_pass_manager : Flag<["-"], "fno-legacy-pass-manager">,
-  Group<f_clang_Group>, Flags<[CC1Option, NoArgumentUnused]>;
-def fexperimental_new_pass_manager : Flag<["-"], "fexperimental-new-pass-manager">,
-  Group<f_clang_Group>, Flags<[CC1Option]>, Alias<fno_legacy_pass_manager>;
 def fexperimental_strict_floating_point : Flag<["-"], "fexperimental-strict-floating-point">,
   Group<f_clang_Group>, Flags<[CC1Option]>,
   HelpText<"Enables experimental strict floating point in LLVM.">,