[buffer_cache] Simplify GPU fence synchronization and remove GPU buffer readback (#4477)

- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
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-------------------

This is understood to improve GPU synchronization within the buffer cache in certain edge cases.

GPU Fence Strict is no longer necessary. We now apply the stronger synchronization only in the specific case that actually requires it.

The GPU Buffer Readback has been removed, as it is no longer needed following PR #4473.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4477
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>

src/common/settings.h

@@ -525,7 +525,7 @@ struct Values {
     SwitchableSetting<GpuFenceBehavior, true> gpu_fence_behavior{linkage,
                                                                  GpuFenceBehavior::Default,
                                                                  GpuFenceBehavior::Default,
-                                                                 GpuFenceBehavior::Strict,
+                                                                 GpuFenceBehavior::Accurate,
                                                                  "gpu_fence_behavior",
                                                                  Category::RendererAdvanced,
                                                                  Specialization::Default,
@@ -655,13 +655,6 @@ struct Values {
 
     SwitchableSetting<bool> rescale_hack{linkage, false, "rescale_hack",
                                          Category::RendererHacks};
-    SwitchableSetting<bool> enable_gpu_buffer_readback{linkage,
-                                                       false,
-                                                       "enable_gpu_buffer_readback",
-                                                       Category::RendererAdvanced,
-                                                       Specialization::Default,
-                                                       true,
-                                                       true};
 
     SwitchableSetting<bool> use_asynchronous_shaders{linkage, false, "use_asynchronous_shaders",
                                                      Category::RendererHacks};
@@ -979,7 +972,6 @@ bool IsDMALevelSafe();
 bool IsGPUFenceBehaviorDefault();
 bool IsGPUFenceBehaviorBalanced();
 bool IsGPUFenceBehaviorAccurate();
-bool IsGPUFenceBehaviorStrict();
 
 bool IsFastmemEnabled();
 void SetNceEnabled(bool is_64bit);