Remove extra GMG output

[gassmoeller]

The GMG solver always outputs an additional line in the log.txt and screen output that informs the user about the level of vectorization, even though this is already stated (in less detail) in the ASPECT header. This is slightly annoying, and moreover, because this line is not removed from the test output it causes issues if different testers use different vectorizations (e.g. the Jenkins OSX tester, which creates different output than the Jenkins tester for the quick_mpi test if run with GMG).

Therefore I propose to remove the extra line, and always output the vectorization information in the header. This looks cleaner and resolves the tester problems in #5211.

Previously the output would look like this:

-----------------------------------------------------------------------------
--                             This is ASPECT                              --
-- The Advanced Solver for Planetary Evolution, Convection, and Tectonics. --
-----------------------------------------------------------------------------
--     . version 2.6.0-pre
--     . using deal.II 9.5.1
--     .       with 32 bit indices and vectorization level 1 (128 bits)
--     . using Trilinos 13.2.0
--     . using p4est 2.3.2
--     . using Geodynamic World Builder 0.6.0
--     . running in DEBUG mode
--     . running with 1 MPI process
-----------------------------------------------------------------------------

Loading shared library <./libquick_mpi.debug.so>

Vectorization over 2 doubles = 128 bits (SSE2), VECTORIZATION_LEVEL=1
-----------------------------------------------------------------------------
-- For information on how to cite ASPECT, see:
--   https://aspect.geodynamics.org/citing.html?ver=2.6.0-pre&mf=1&sha=&src=code
-----------------------------------------------------------------------------
Number of active cells: 16 (on 3 levels)
Number of degrees of freedom: 268 (162+25+81)

Now it looks like this (ignore the changed vectorization information, I ran the output above inside the docker container and the one below on my native OS):

-----------------------------------------------------------------------------
--                             This is ASPECT                              --
-- The Advanced Solver for Planetary Evolution, Convection, and Tectonics. --
-----------------------------------------------------------------------------
--     . version 2.6.0-pre (remove_gmg_extra_line, e85628aaf)
--     . using deal.II 9.5.2
--     .       with 64 bit indices
--     .       with vectorization level 3 (AVX512, 8 doubles, 512 bits)
--     . using Trilinos 13.2.0
--     . using p4est 2.3.2
--     . using Geodynamic World Builder 0.6.0
--     . running in DEBUG mode
--     . running with 1 MPI process
-----------------------------------------------------------------------------

Loading shared library <./libquick_mpi.debug.so>

-----------------------------------------------------------------------------
-- For information on how to cite ASPECT, see:
--   https://aspect.geodynamics.org/citing.html?ver=2.6.0-pre&sha=e85628aaf&src=code
-----------------------------------------------------------------------------
Number of active cells: 16 (on 3 levels)
Number of degrees of freedom: 268 (162+25+81)

[MFraters]

I like this change, but it would be good for @tjhei to also review this.

[bangerth]

I had noticed this at some point before as well and found it odd. I like this clean-up.