Remove serial number

It doesn't work with windows. It seems that the USB device goes into low
power state and then the serial number string descriptor cannot be read.

.gitignore

@@ -1,3 +1,2 @@
 /target
 /.direnv
-/src/serial_number.rs

src/main.rs

@@ -20,8 +20,6 @@ use usbd_storage::subclass::Command;
 use usbd_storage::transport::bbb::{BulkOnly, BulkOnlyError};
 use usbd_storage::transport::TransportError;
 
-mod serial_number;
-
 const DISK_BLOCK_SIZE: u32 = 512;
 const DISK_BLOCK_NUM: u32 = 256;
 
@@ -112,8 +110,7 @@ fn main() -> ! {
     let mut usb_device = UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0xcafe, 0x4002))
         .strings(&[StringDescriptors::new(LangID::EN)
             .manufacturer("jalr")
-            .product("RAM Mass Storage")
-            .serial_number(serial_number::SERIAL)])
+            .product("RAM Mass Storage")])
         .unwrap()
         .device_class(0x08)
         .self_powered(false)

src/serial_number.rs.example

@@ -1 +0,0 @@
-pub const SERIAL: &str = "example-4711";