Remove deprecated functions

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: -2.59 :warning:

Comparison is base (2aedeaf) 85.35% compared to head (2860df3) 82.77%.

:exclamation: Current head 2860df3 differs from pull request most recent head 9852278. Consider uploading reports for the commit 9852278 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## v4 #496 +/- ## ============================================ - Coverage 85.35% 82.77% -2.59% ============================================ Files 114 58 -56 Lines 9929 5607 -4322 Branches 617 0 -617 ============================================ - Hits 8475 4641 -3834 + Misses 1431 966 -465 + Partials 23 0 -23 ``` | [Impacted Files](https://app.codecov.io/gh/dmlc/treelite/pull/496?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dmlc) | Coverage Δ | | |---|---|---| | [include/treelite/c\_api\_error.h](https://app.codecov.io/gh/dmlc/treelite/pull/496?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dmlc#diff-aW5jbHVkZS90cmVlbGl0ZS9jX2FwaV9lcnJvci5o) | `100.00% <ø> (ø)` | | | [python/treelite/frontend.py](https://app.codecov.io/gh/dmlc/treelite/pull/496?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dmlc#diff-cHl0aG9uL3RyZWVsaXRlL2Zyb250ZW5kLnB5) | `72.78% <ø> (-5.35%)` | :arrow_down: | | [src/c\_api/c\_api\_error.cc](https://app.codecov.io/gh/dmlc/treelite/pull/496?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dmlc#diff-c3JjL2NfYXBpL2NfYXBpX2Vycm9yLmNj) | `41.66% <ø> (ø)` | | | [python/treelite/\_\_init\_\_.py](https://app.codecov.io/gh/dmlc/treelite/pull/496?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dmlc#diff-cHl0aG9uL3RyZWVsaXRlL19faW5pdF9fLnB5) | `100.00% <100.00%> (ø)` | | | [src/c\_api/c\_api.cc](https://app.codecov.io/gh/dmlc/treelite/pull/496?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dmlc#diff-c3JjL2NfYXBpL2NfYXBpLmNj) | `75.08% <100.00%> (-5.39%)` | :arrow_down: | ... and [44 files with indirect coverage changes](https://app.codecov.io/gh/dmlc/treelite/pull/496/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dmlc)

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