build(deps): remove unused lru-cache dependency

[HeversonSilva-gif]

lru-cache@^5.1.1 is declared in dependencies but is not imported anywhere in the
project. Its only occurrence in the whole repository is the package.json line itself.

Everyone who installs docsify-cli gets it, and nothing ever loads it.

Verified at b9d118f on Node 20.20.0 / npm 10.8.2, Windows:

• git grep -E "(from|require\(|import\()\s*['\"]lru-cache" returns nothing, and a plain
  git grep for lru-cache or LRU outside the lockfile matches only package.json:61.

• npm run build (rollup) after the change: exit 0, lib/cli.js → bin/docsify created as
  before. Nothing was being bundled from it either.

• npm test before the change: 9 tests failed. After the change: 9 tests failed. The
  set of failing titles is identical, diffed rather than counted:

  cli › shows up help message without any args
  cli › shows help with -h flag
  cli › shows help with --help flag
  cli › shows version information with -v flag
  cli › shows version information with --version flag
  cli › rejects promise due to error on passing in an unknown command
  commands › generate › generate _sidebar.md
  commands › init › generates docs directory
  commands › init › force generates docs directory with --local flag
  

  Those 9 are pre-existing on this machine and unrelated to this change — they are the
  e2e tests that shell out, and they fail the same way on a clean checkout. pretest runs
  eslint ., which is clean on both sides.

• npm install reports removed 2 packages: lru-cache and yallist, which came in only
  as its dependency.

I have not touched anything else. If you would rather I re-run the suite somewhere the e2e
tests pass before this is merged, I'm happy to, but the failing set being identical is what
tells you the change is inert.

[sy-records]

Thanks.

It was previously referenced in SSR, but now that SSR has been removed, it is no longer needed.