[vulkan] Don't free command buffers before destroying the pool. (#4059)

Calling `vkDestroyCommandPool` automatically frees all command buffers allocated
from that pool, so there is no need for `Device::destroy_command_encoder` to
explicitly call `vkFreeCommandBuffers` on the `CommandEncoder`'s `free` and
`discarded` lists.

CHANGELOG.md

@@ -70,6 +70,10 @@ By @Valaphee in [#3402](https://github.com/gfx-rs/wgpu/pull/3402)
 - Validate `DownlevelFlags::READ_ONLY_DEPTH_STENCIL`. By @teoxoy in [#4031](https://github.com/gfx-rs/wgpu/pull/4031)
 - Add validation in accordance with WebGPU `setViewport` valid usage for `x`, `y` and `this.[[attachment_size]]`. By @James2022-rgb in [#4058](https://github.com/gfx-rs/wgpu/pull/4058)
 
+#### Vulkan
+
+- Don't bother calling `vkFreeCommandBuffers` when `vkDestroyCommandPool` will take care of that for us. By @jimblandy in [#4059](https://github.com/gfx-rs/wgpu/pull/4059)
+
 ### Bug Fixes
 
 #### General

wgpu-hal/src/vulkan/device.rs

@@ -1193,16 +1193,10 @@ impl crate::Device<super::Api> for super::Device {
     }
     unsafe fn destroy_command_encoder(&self, cmd_encoder: super::CommandEncoder) {
         unsafe {
-            if !cmd_encoder.free.is_empty() {
-                self.shared
-                    .raw
-                    .free_command_buffers(cmd_encoder.raw, &cmd_encoder.free)
-            }
-            if !cmd_encoder.discarded.is_empty() {
-                self.shared
-                    .raw
-                    .free_command_buffers(cmd_encoder.raw, &cmd_encoder.discarded)
-            }
+            // `vkDestroyCommandPool` also frees any command buffers allocated
+            // from that pool, so there's no need to explicitly call
+            // `vkFreeCommandBuffers` on `cmd_encoder`'s `free` and `discarded`
+            // fields.
             self.shared.raw.destroy_command_pool(cmd_encoder.raw, None);
         }
     }