include: Removed :: from symbol names in comments.

This isn't C++ code, so there's no need to append global symbols with two
colons. It looks ugly.

I _did_ leave them for actual C++ things in WinRT-specific comments and other
places, like a reference to a Perl class thing.

Also, even though it's not valid C, it's a useful expression to say
`StructType::SpecificField`, so I left those alone, too.

include/SDL3/SDL_sensor.h

@@ -44,7 +44,7 @@ extern "C" {
  *  SDL_sensor.h
  *
  *  In order to use these functions, SDL_Init() must have been called
- *  with the ::SDL_INIT_SENSOR flag.  This causes SDL to scan the system
+ *  with the SDL_INIT_SENSOR flag.  This causes SDL to scan the system
  *  for sensors, and load appropriate drivers.
  */