Revert "std.os: add INVALID_SOCKET (#12081)"

This reverts commit 0f01e81.

This does not belong in `std.posix`, and it is already provided at
`std.os.windows.ws2_32.INVALID_SOCKET`.

See related issue #5019.

Author: andrewrk

lib/std/os.zig

@@ -235,7 +235,6 @@ pub const RelativePathWasi = struct {
 };
 
 pub const socket_t = if (builtin.os.tag == .windows) windows.ws2_32.SOCKET else fd_t;
-pub const INVALID_SOCKET = if (builtin.os.tag == .windows) windows.ws2_32.INVALID_SOCKET else @as(socket_t, -1);
 
 /// See also `getenv`. Populated by startup code before main().
 /// TODO this is a footgun because the value will be undefined when using `zig build-lib`.