docs: improvements to source code documentation (#1236)

src/platform/windows/misc.h

@@ -1,5 +1,4 @@
-#ifndef SUNSHINE_WINDOWS_MISC_H
-#define SUNSHINE_WINDOWS_MISC_H
+#pragma once
 
 #include <chrono>
 #include <string_view>
@@ -18,5 +17,3 @@ namespace platf {
   std::chrono::nanoseconds
   qpc_time_difference(int64_t performance_counter1, int64_t performance_counter2);
 }  // namespace platf
-
-#endif