Breaking change: remove deprecated flag for enabling MSVC support

With the path length limitations from Bazel fixed, we ended up reversing course on this plan.  We will continue to support MSVC and this flag hasn't done anything for a few releases.

PiperOrigin-RevId: 853482413

Author: mkruskal-google

build_defs/BUILD.bazel

@@ -49,13 +49,6 @@ platform(
     ],
 )
 
-config_setting(
-    name = "protobuf_allow_msvc",
-    values = {
-        "define": "protobuf_allow_msvc=true",
-    },
-)
-
 selects.config_setting_group(
     name = "config_msvc",
     match_any = [