Drop two type definition modules that are no longer needed

`npm` pointed out that:

  npm warn deprecated @types/json-stable-stringify@1.2.0: This is a stub
    types definition. json-stable-stringify provides its own type
    definitions, so you do not need this installed.
  npm warn deprecated @types/marked@6.0.0: This is a stub types
    definition. marked provides its own type definitions, so you do not
    need this installed.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

package-lock.json

@@ -54,10 +54,8 @@
     "@types/html-to-text": "^9.0.4",
     "@types/imap-simple": "^4.2.10",
     "@types/jest": "^30.0.0",
-    "@types/json-stable-stringify": "^1.2.0",
     "@types/jsonwebtoken": "^9.0.10",
     "@types/mailparser": "^3.4.6",
-    "@types/marked": "^6.0.0",
     "@types/node": "^24.2.1",
     "@types/nodemailer": "^6.4.17",
     "@types/rfc2047": "^2.0.3",