Don't use markdown in VKit comments

[pongad]

Comments like

the `x-goog-api-client` header

should have the backticks removed.

[bjwatson]

Related PRs for Python:

• https://github.com/googleapis/toolkit/issues/222
• [Python] Sphinx cannot handle indentation in proto comments #402

[geigerj]

See also

https://github.com/googleapis/toolkit/blob/master/src/main/java/com/google/api/codegen/CommentPatterns.java

and

https://github.com/googleapis/toolkit/blob/master/src/main/java/com/google/api/codegen/py/PythonSphinxCommentFixer.java

for what Python does here. As discussed offline it would eventually be good to get a proper Markdown processor hooked up to this, like what we have internally.

[bjwatson]

@pongad @garrettjonesgoogle This seems like a duplicate of #331. I like how 331 is phrased better, because I want to make use of the backticks as a hint for code formatting, rather than just removing them (which only makes sense if a language's doc system has zero support for code formatting).

Unless I'm missing something subtle, one of these should be closed.

[garrettjonesgoogle]

Yeah, probably close this one (475).

[pongad]

Duplicate of #331