refact(rivet): disallow function declarations with extern

Author: StunxFS

lib/rivet/src/parser/decls.ri

@@ -189,12 +189,6 @@ extend Parser {
                         }
                     }
                     self.expect(.Rbrace);
-                } else if self.accept(.KwFunc) {
-                    decls.push(self.parse_func_decl(
-                        doc_comment, annotations, is_public,
-                        annotations.has("unsafe") or abi != .Rivet,
-                        abi
-                    ));
                 } else {
                     report.error("invalid external declaration", pos);
                 }

rivetc/src/parser.py

@@ -220,13 +220,6 @@ def parse_decl(self):
                     if self.tok.kind == Kind.Rbrace:
                         break
                 self.expect(Kind.Rbrace)
-            elif self.accept(Kind.KwFunc):
-                protos.append(
-                    self.parse_func_decl(
-                        doc_comment, annotations, is_public,
-                        annotations.has("unsafe") or abi != sym.ABI.Rivet, abi
-                    )
-                )
             else:
                 report.error("invalid external declaration", pos)
             self.inside_extern = False