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Example

Betula alba var. pendula
Betula alba subsp. pendula

I'm thinking to erase all those (var., subsp., ...), they only create confusion.
I have seen online databases that did that, can't pull out of head which.

Opinions ?

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Betula is governed by the botanical code, which I do not understand.

Varieties are no longer allowed by the code of zoological nomenclature. Varieties proposed before 1961 may be treated as subspecies.

Subspecies are rarely used for Diptera. Mammalogists, on the other hand, love subspecies. Slovenia is near the intersection of 3 of the 22 subspecies of Sciurus vulgaris -- the central European fuscoater ("a bright red form, with a white venter"), the western Balkan lilaeus ("a generally brownish form"), and Italian alpinus ("an intense russet brown over the dorsum").

I only note subspecies when I consider the difference interesting. For example, 2 of the 21 subspecies of Tamias minimus are colored tan instead of brown to match the color of the ground where they live in the "badlands" of western North America.

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I don't know about the botanical rules, but you can find the online zoological rules (the 'International Code for Zoological Nomenclature' or 'ICZN' or simply 'the Code' ) right here.

If you would remove the abbreviation 'var.', you are in fact upgrading the status of the taxon to subspecies.

For example, if you write
Canthon septemmaculatus var. lineatus
you are using an infrasubspecific name (a name denoting a taxonomic level lower than subspecies). Such names are currently not governed by the ICZN.

If you remove 'var.', you get
Canthon septemmaculatus lineatus
which is a subspecific name and thus governed by the ICZN. Any name behind a specific name is automatically a subspecific name, unless it is clearly denoted as a var(iety), ab(beration), f(orma) and so on. See the Code for more details and the correct abbreviations.

I would thus suggest you remove the abbreviation 'subsp.' because it does not add any additional info, but I recommend you leave the other abbreviations in place or remove those infraspecific names (and keeep the example as Canthon septemmaculatus). Of course, varieties can be upgraded tot subspecies, subspecies upgraded to species, abberations synonymized with species etc. etc., and taxonomists may not agree with eachothers views (think e.g. of splitters versus lumpers). You should always best use the most recent literature as well as your own common sense as to which view you adopt.

Keep in mind that most subspecific and infrasubspecific names are used for large and colourful species (butterflies, flower chafers etc.), while 'boring' small brown bugs will almost never get a name beyond specific level, even though their infraspecific genetic variation may be larger. I guess such names have often more to do with aesthetics and profits than with taxonomy.