Standarise compiler scripts

[sergisiso]

I would be good to clean up the compiler scripts, currently they have some inconsistencies:

• Different compiler set up by default different compilation features (e.g. -g is set on some but not on others). For benchmarking it would be better if all are as similar as possible.
• the (*_acc.sh) are not needed anymore because e.g. nvidia.sh already sets a ACCFLAGS for OpenACC compilation.
• the reset.sh does not clean up the environment variables that we have added more recently.

[LonelyCat124]

Related - when using intel.sh it ignores F90FLAGS in the environment (at least for the tracer advection benchmark) resulting in no vectorisation flags if you place them there.