Use the cargo.eclass-provided local source for mlua-extra

cargo.eclass overrides the Git dependency with a local path via
[patch], so Cargo expects the package to have no Git source in Cargo.lock.
This keeps --locked builds compatible with the Portage-managed source.
--- ../Cargo.lock	2026-09-28 14:49:48.263838241 +0300
+++ ../Cargo.lock	2026-09-28 14:50:00.406453380 +0300
@@ -1738,7 +1738,6 @@
 [[package]]
 name = "mlua-extra"
 version = "0.1.0"
-source = "git+https://github.com/hypengw/mlua-extra?rev=df1d282170dd1718b8aeff405638c18cedd435ca#df1d282170dd1718b8aeff405638c18cedd435ca"
 dependencies = [
  "base64",
  "cookie_store",