[mlir][sparse] Fix memory leaks (part 4)

This commit fixes memory leaks in sparse tensor integration tests by
adding `bufferization.dealloc_tensor` ops.

Note: Buffer deallocation will be automated in the future with the
ownership-based buffer deallocation pass, making `dealloc_tensor`
obsolete (only codegen path, not when using the runtime library).

This commit fixes the remaining memory leaks in the MLIR test suite.
`check-mlir` now passes when built with ASAN.