Lynis: Suggestion: Harden the system by removing unneeded compilers. This can decrease the chance of customized trojans, ... [test:HRDN-7220]

In the case Lynis list the following suggestion:

Suggestion: Harden the system by removing unneeded compilers. This can decrease the chance of customized trojans, backdoors and rootkits to be compiled and installed [test:HRDN-7220]

Then you have to remove the compilers.
To do so do the following:

sudo apt-get remove binutils && sudo apt-get autoremove && sudo apt-get clean