Remove duplicate CLI function documentation

Eliminated redundant sections for `format_size` and `validate_compression_level` in the CLI documentation to improve clarity and avoid repetition.

docs/api/cli.md

@@ -40,15 +40,3 @@ The command-line interface module provides functions for the tzst CLI tool.
 ```{eval-rst}
 .. autofunction:: tzst.cli.validate_compression_level
 ```
-
-### format_size
-
-```{eval-rst}
-.. autofunction:: tzst.cli.format_size
-```
-
-### validate_compression_level
-
-```{eval-rst}
-.. autofunction:: tzst.cli.validate_compression_level
-```