We are planning to enable -Wextra-semi flag in our project but some
header files in gRPC have extra semicolons that violates the check and
blocks us from enabling the flag.
This change removes unnecessary semicolons in the code. Note that having
semicolon after the GRPC_ABSTRACT macro technically also violates the
check, but it's fine for us since they are not used in public headers,
and it will be confusing to have lines ending only with GRPC_ABSTRACT,
so I keep them as-is.
Yuwei Huang