fix: drop unused riscv64 enable option

Fixes #2509

Author: Xeonacid

bin/generate_schema.py

@@ -33,7 +33,6 @@
     description: How to inherit the parent's value.
   enable:
     enum:
-      - cpython-experimental-riscv64
       - cpython-freethreading
       - cpython-prerelease
       - graalpy

cibuildwheel/resources/cibuildwheel.schema.json

@@ -13,7 +13,6 @@
     },
     "enable": {
       "enum": [
-        "cpython-experimental-riscv64",
         "cpython-freethreading",
         "cpython-prerelease",
         "graalpy",

cibuildwheel/selector.py

@@ -29,7 +29,6 @@ class EnableGroup(StrEnum):
     Groups of build selectors that are not enabled by default.
     """
 
-    CPythonExperimentalRiscV64 = "cpython-experimental-riscv64"
     CPythonFreeThreading = "cpython-freethreading"
     CPythonPrerelease = "cpython-prerelease"
     GraalPy = "graalpy"