graphics: serialize pipeline cache through its renderer owner

src/graphics/host_gpu/renderer/pipeline/pipelineCache.h

@@ -4,7 +4,6 @@
 #include "common/abi.h"
 #include "common/assert.h"
 #include "common/common.h"
-#include "common/threads.h"
 #include "graphics/host_gpu/renderer/renderTarget.h"
 #include "graphics/host_gpu/vulkanCommon.h"
 #include "graphics/shader/shader.h"
@@ -103,6 +102,7 @@ struct ShaderProgram {
 	explicit operator bool() const { return id != 0 && module != nullptr; }
 };
 
+// The owning renderer serializes access, including saves while the GPU is running.
 class PipelineCache {
 public:
 	explicit PipelineCache(GraphicContext& graphics);
@@ -179,7 +179,6 @@ private:
 	std::unordered_map<GraphicsPipelineKey, std::unique_ptr<Pipeline>, GraphicsPipelineKeyHash>
 	                                                        m_graphics_pipelines;
 	std::unordered_map<uint64_t, std::unique_ptr<Pipeline>> m_compute_pipelines;
-	Common::Mutex m_mutex;
 
 	void InitializeDriverCache();
 };