refactor: remove unnecessary functions from getTypeServices

[JasonWeinzierl]

These utility functions are unused or replaceable with built-in ESLintUtils.getTypeServices or ts-api-utils.

[github-actions]

LCOV of commit 5b8a848 during .github/workflows/ci.yml #76

Summary coverage rate:
  lines......: 96.3% (3270 of 3397 lines)
  functions..: 94.7% (197 of 208 functions)
  branches...: 91.2% (619 of 679 branches)

Files changed coverage rate:
                                         |Lines       |Functions  |Branches    
  Filename                               |Rate     Num|Rate    Num|Rate     Num
  =============================================================================
  src/etc/get-type-services.ts           | 100%     67| 100%    10|91.7%     24
  src/rules/no-cyclic-action.ts          |89.0%    109| 100%     4|68.4%     19
  src/rules/no-unbound-methods.ts        |97.2%     72| 100%     6|92.9%     14
  src/rules/no-unsafe-subject-next.ts    | 100%     54| 100%     1| 100%     14
  src/rules/throw-error.ts               | 100%     51| 100%     3| 100%      7