help: remove note about v2 backend (#6364)

cmd/v/help/build.txt

@@ -29,8 +29,6 @@ The build flags are shared by the build and run commands:
       * `c` (default)       - V outputs C source code which is passed to a C compiler to be compiled.
       * `js`                - V outputs JS source code which can be passed to NodeJS to be ran.
       * `x64`               - V outputs Linux 64-bit executable directly (highly experimental!).
-      * `v2`/`experimental` - Invokes the experimental AST-powered V compiler that will replace the
-                              current backends when finished
 
    -d <flag>[=<value>], -define <flag>[=<value>]
       Define the provided flag.

cmd/v/help/fmt.txt

@@ -29,4 +29,3 @@ Environment Variables:
   VDIFF_OPTIONS   A set of command-line options to be sent immediately after the
                   `diff` command. e.g.
                   VDIFF_OPTIONS="-W 80 -y" v fmt -diff path/to/file.v /tmp/v/vfmt_file.v
-