[ci] remove unnecessary package installations in CI

[jameslamb]

Reduces the set of packages installed in CI jobs.

.ci/setup.sh is responsible for installing some system packages that are common across most CI jobs. Some of the things installed there have been carried around in LightGBM's CI scripts for years, since back when the project used Travis (#3672, #1669).

Some of them are no longer necessary. For example, tools like netcat and iputils-ping provide some useful tools for debugging networking issues, but those tools aren't invoked in this project's CI scripts.

Benefits of these changes:

• faster builds
• reduced risk of build failures due to installation problems

[jameslamb]

With a --no-install-recommends added here, the C++ tests fail:

[ 70%] Building CXX object CMakeFiles/lightgbm_objs.dir/src/treelearner/serial_tree_learner.cpp.o
In file included from /__w/1/s/src/treelearner/linear_tree_learner.cpp:7:
In file included from /__w/1/s/external_libs/eigen/Eigen/Dense:1:
In file included from /__w/1/s/external_libs/eigen/Eigen/Core:22:
In file included from /__w/1/s/external_libs/eigen/Eigen/src/Core/util/ConfigureVectorization.h:346:
In file included from /usr/lib/llvm-17/lib/clang/17/include/emmintrin.h:17:
In file included from /usr/lib/llvm-17/lib/clang/17/include/xmmintrin.h:31:
/usr/lib/llvm-17/lib/clang/17/include/mm_malloc.h:32:40: error: 'alloc_align' attribute parameter 1 is out of bounds
   32 |                                        __alloc_align__(2)))

https://dev.azure.com/lightgbm-ci/lightgbm-ci/_build/results?buildId=16401&view=results

I'm unsure why. For now, just letting apt-get install the other recommended packages seems to resolve that, so I think we should continue doing that.

[jameslamb]

I believe that != "mpi" was just a shorter way to represent some other subset of jobs and that this has been carried forward unnecessarily from older versions of these build scripts.

Proposing removing this condition to simplify the scripts a bit... if the job has COMPILER=gcc set, we need to install gcc.

[jameslamb]

Thanks @borchero ! I'm going to keep trying to simplify these builds. There is a lot of stuff that's built up over the years (much of it written by me 😅 ) that's worth re-examining.