replace google::protobuf::int64 by int64_t

[gulu-goolu]

google::protobuf::int64 has been removed.

What problem does this PR solve?

Issue Number:

Problem Summary:

What is changed and the side effects?

Changed:

Side effects:

• Performance effects:

• Breaking backward compatibility:

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Samrose-Ahmed]

Forgot to fix these in iobuf.cpp as well:

brpc/src/butil/iobuf.cpp

Line 1872 in b990d5c

google::protobuf::int64 IOBufAsZeroCopyInputStream::ByteCount() const {

brpc/src/butil/iobuf.cpp

Line 1993 in b990d5c

google::protobuf::int64 IOBufAsZeroCopyOutputStream::ByteCount() const {