disable doxygen searchengine and latex generation

The current API docs for Groovy are around **26 GB**.

By removing the generated searchengine in doxygen (the small search box in the top right corner at e.g. http://docs.ros.org/hydro/api/roscpp/html/index.html) the amount would be significantly reduced to **6.9 GB**.

Additionally I am not sure why we generate latex docs in the first place (e.g. http://docs.ros.org/hydro/api/roscpp/html/latex/) - likely because it is the default in doxygen. By disabling this we another 20% in size resulting in only **5.7 GB**.

After this has been merged (and all doc jobs have been executed) it must be verified that the already available generated search/latex documentation is actually removed form the server.