genesys: use usleep instead of std::this_thread::sleep_for to re-enable thread less compile

Fixes:

  genesys/scanner_interface_usb.cpp: In member function ‘virtual void genesys::ScannerInterfaceUsb::sleep_us(unsigned int)’:
  genesys/scanner_interface_usb.cpp:484:10: error: ‘std::this_thread’ has not been declared
    484 |     std::this_thread::sleep_for(std::chrono::microseconds{microseconds});
        |          ^~~~~~~~~~~

Signed-off-by: Peter Seiderer <ps.report@gmx.net>

backend/genesys/scanner_interface_usb.cpp

@@ -43,7 +43,6 @@
 
 #include "scanner_interface_usb.h"
 #include "low.h"
-#include <thread>
 
 namespace genesys {
 
@@ -481,7 +480,7 @@ void ScannerInterfaceUsb::sleep_us(unsigned microseconds)
     if (sanei_usb_is_replay_mode_enabled()) {
         return;
     }
-    std::this_thread::sleep_for(std::chrono::microseconds{microseconds});
+    usleep(microseconds);
 }
 
 void ScannerInterfaceUsb::record_progress_message(const char* msg)