docs: remove starchart.cc embed (#425)

starchart.cc is rate limited and rendering a broken image.

Refs: caarlos0/starcharts#260

Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: caarlos0

README.md

@@ -150,7 +150,3 @@ Eventual bug fixes will keep being merged.
 ## Related projects
 
 - [envdoc](https://github.com/g4s8/envdoc) - generate documentation for environment variables from `env` tags
-
-## Stargazers over time
-
-[![Stargazers over time](https://starchart.cc/caarlos0/env.svg?variant=adaptive)](https://starchart.cc/caarlos0/env)