Code refactor on rdsn module

[acelyc111]

Inspired by and thanks to rdsn, the Pegasus project could be developed nowadays.

The xiaomi/rdsn repo has been merged into apache/pegasus for months, now I consider the Pegasus branch rdsn is deeply modified and only used for Pegasus, and it's very hard and maybe meaningless to contribute these changes back upstream, so I'm planning to continue the work of refactoring rdsn module, including:

• remove the C language sopporting
• make it as a internel module but not a public library
• ...