src: remove unnecessary semicolons
Refs https://github.com/electron/electron/pull/36818.
These extra semicolons cause build failures in Electron, e.g.
In file included from ../../third_party/electron_node/src/node_util.cc:1:
../../third_party/electron_node/src/node_util.h:15:32: error: extra ';' inside a class [-Werror,-Wextra-semi]
SERIALIZABLE_OBJECT_METHODS();
^
1 error generated.