Remove unused dependencies

These dependencies of the top-level `mdbook` package are not directly
used. They are used transitively, so this makes little difference, but
helps to convey what is actually needed.

Cargo.lock

@@ -954,10 +954,8 @@ dependencies = [
  "mdbook-core",
  "mdbook-driver",
  "mdbook-html",
- "mdbook-markdown",
  "mdbook-preprocessor",
  "mdbook-renderer",
- "mdbook-summary",
  "notify",
  "notify-debouncer-mini",
  "opener",
@@ -969,7 +967,6 @@ dependencies = [
  "snapbox",
  "tempfile",
  "tokio",
- "toml",
  "tower-http",
  "tracing",
  "tracing-subscriber",

Cargo.toml

@@ -94,12 +94,7 @@ clap_complete.workspace = true
 mdbook-core.workspace = true
 mdbook-driver.workspace = true
 mdbook-html.workspace = true
-mdbook-markdown.workspace = true
-mdbook-preprocessor.workspace = true
-mdbook-renderer.workspace = true
-mdbook-summary.workspace = true
 opener.workspace = true
-toml.workspace = true
 tracing.workspace = true
 tracing-subscriber.workspace = true
 
@@ -118,6 +113,8 @@ tower-http = { workspace = true, features = ["fs", "trace"], optional = true }
 
 [dev-dependencies]
 glob.workspace = true
+mdbook-preprocessor.workspace = true
+mdbook-renderer.workspace = true
 regex.workspace = true
 select.workspace = true
 semver.workspace = true