memory: Drop superseded allocator-based create/destroy functions

[stotko]

In #251, new allocator-based overloads to the create/destroy memory functions have been added to support custom allocators throughout all containers of the library. Since allocator_traits has been extended and adopted by the containers, these older functions are not used anymore and primarily only point to allocator_traits anyways. Drop them to streamline the memory API and reduce the maintenance burden.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.03 :warning:

Comparison is base (96bab15) 97.29% compared to head (1e79021) 97.27%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #369 +/- ## ========================================== - Coverage 97.29% 97.27% -0.03% ========================================== Files 31 31 Lines 2480 2456 -24 ========================================== - Hits 2413 2389 -24 Misses 67 67 ``` | [Impacted Files](https://app.codecov.io/gh/stotko/stdgpu/pull/369?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko) | Coverage Δ | | |---|---|---| | [src/stdgpu/impl/memory\_detail.h](https://app.codecov.io/gh/stotko/stdgpu/pull/369?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL21lbW9yeV9kZXRhaWwuaA==) | `99.01% <100.00%> (-0.11%)` | :arrow_down: |

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