Revert "fix: rm ocurl dependency (unused atm)"

This reverts commit 11970e8.

abella.opam

@@ -21,6 +21,7 @@ depends: [
   "base64"    { >= "3.5.1" }
   "cmdliner"  { >= "1.2.0" }
   "menhir"    { >= "20211012" }
+  "ocurl"     { >= "0.9.2" }
   "re"        { >= "1.11.0" }
   "yojson"    { >= "2.1.1" }
   "dune"      { >= "3.7" }