Housekeeping

[willtebbutt]

A moderate amount of un-used code has accrued throughout the codebase. This PR is going to go through and remove as much stuff as possible.

[github-actions]

Performance Ratio:

┌────────────────────────────┬────────┬─────────┬─────────────┬─────────┐
│                      Label │  Tapir │  Zygote │ ReverseDiff │  Enzyme │
│                     String │ String │  String │      String │  String │
├────────────────────────────┼────────┼─────────┼─────────────┼─────────┤
│                        sum │   30.6 │   0.324 │        2.23 │    0.63 │
│                       _sum │   6.64 │   495.0 │        28.3 │   0.121 │
│                   kron_sum │   80.4 │    3.39 │       204.0 │    24.3 │
│              kron_view_sum │   93.3 │    11.2 │       230.0 │    8.36 │
│      naive_map_sin_cos_exp │   4.22 │ missing │        8.85 │    2.79 │
│            map_sin_cos_exp │   4.61 │    1.74 │        7.64 │    3.44 │
│      broadcast_sin_cos_exp │   4.35 │    2.65 │        1.69 │    2.88 │
│                 simple_mlp │    9.1 │     3.2 │        11.2 │    3.32 │
│                     gp_lml │   16.1 │    4.34 │     missing │ missing │
│ turing_broadcast_benchmark │   6.07 │ missing │        34.6 │ missing │
└────────────────────────────┴────────┴─────────┴─────────────┴─────────┘