Docs: Remove section about overriding cache dir

The env var `TEALDEER_CACHE_DIR` is deprecated. The new way to configure
the cache dir is documented in the "[directories]" section.

docs/src/config.md

@@ -52,11 +52,3 @@ auto_update = true
 The directory where the configuration file resides may be overwritten by the
 environment variable `TEALDEER_CONFIG_DIR`. Remember to use an absolute path.
 Variable expansion will not be performed on the path.
-
-## Override Cache Directory
-
-Similarly, the cache directory where the pages are downloaded to, also follows
-OS conventions. On Linux, it will usually be at `~/.cache/tealdeer/`. The path
-can be overwritten using the environment variable `TEALDEER_CACHE_DIR`.
-Remember to use an absolute path. Variable expansion will not be performed on
-the path.