Update base for Update on "[ET-VK] Removing unnecessary and redundant members from StagingBuffer."

This diff removes unnecessary and redundant members from the StagingBuffer class in the Vulkan runtime API. Specifically, the `numel_` and `nbytes_` members are removed, as they can be calculated from the `dtype_` member. This simplifies the class and reduces the amount of memory used.

Differential Revision: [D66742613](https://our.internmc.facebook.com/intern/diff/D66742613/)

[ghstack-poisoned]

Author: trivedivivek

backends/vulkan/test/vulkan_compute_api_test.cpp

@@ -1087,8 +1087,8 @@ TEST_F(VulkanComputeAPITest, print_object_sizes) {
 
   // Current known size on 64 bit system: 1040 B
   EXPECT_TRUE(sizeof(vTensor) < 1200);
-  // Current known size on 64 bit system: 32 B
-  EXPECT_TRUE(sizeof(Value) < 40);
+  // Current known size on 64 bit system: 48 B
+  EXPECT_TRUE(sizeof(Value) < 56);
   // Current known size on 64 bit system: 120 B
   EXPECT_TRUE(sizeof(StagingBuffer) < 500);
   // Current known size on 64 bit system: 384 B