proc: Simplify eBPF backend implementation

[chenhengqi]

• Remove standard C headers since we have vmlinux.h already
• Simplify get_goroutine_id() implementation, this reduces a map and thus reduces runtime memory comsumption.

While at it, unify all indention using 4 spaces.

[alexandear]

For the Go code, we have gofmt. Maybe we should use a formatting tool for the C code? E.g. ClangFormat:

clang-format is located in clang/tools/clang-format and can be used to format C/C++/Java/JavaScript/JSON/Objective-C/Protobuf/C# code.

We can check the formatting of the C-code on TeamCity by adding a clang-format step.

[derekparker]

LGTM

Thanks for the patch! In the future however please put formatting changes in a separate PR or at least a separate commit to make it easier to view actual changes from formatting changes.