libcamera: process: Move closeAllFdsExcept()

Remove `closeAllFdsExcept()` from the `Process` class and have it as a
local function since it is not needed "outside" and does not depend on
any part of the `Process` class.

Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/process.h

@@ -45,7 +45,6 @@ public:
 private:
 	LIBCAMERA_DISABLE_COPY_AND_MOVE(Process)
 
-	void closeAllFdsExcept(std::vector<int> v);
 	int isolate();
 	void died(int wstatus);