libcamera: IPAManager: remove instance() and make createIPA() static

As the only usage of IPAManager::instance() is by the pipeline handlers
to call IPAManager::createIPA(), remove the former and make the latter
static. Update the pipeline handlers and tests accordingly.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

include/libcamera/internal/ipa_manager.h

@@ -25,11 +25,9 @@ public:
 	IPAManager();
 	~IPAManager();
 
-	static IPAManager *instance();
-
-	std::unique_ptr<IPAProxy> createIPA(PipelineHandler *pipe,
-					    uint32_t maxVersion,
-					    uint32_t minVersion);
+	static std::unique_ptr<IPAProxy> createIPA(PipelineHandler *pipe,
+						   uint32_t maxVersion,
+						   uint32_t minVersion);
 
 private:
 	static IPAManager *self_;