Dissolve _beh.tsv datatype in favor of _events.tsv

[yarikoptic]

Currently https://bids-specification.readthedocs.io/en/stable/modality-specific-files/behavioral-experiments.html#institution-information words the necessity for _beh.tsv/.json files tandem as

Additionally, events files that do not include the mandatory onset and duration columns can still be included, but should be labeled _beh.tsv rather than _events.tsv.

which makes the need for such files largely superficial. We (with @bendichter) think that it might be better to just use _events.tsv/.json and allow for onset/duration to be n/a in such cases. duration can already be n/a in current BIDS. So it is just a matter of onset and/or thus making it optional altogether.

That would address also ambiguity in current _beh.json which mixed sidecar metadata description (e.g. TaskName and others as listed in https://bids-specification.readthedocs.io/en/stable/modality-specific-files/behavioral-experiments.html#task-information ) and then column descriptors.

edit: 30 datasets in openneuro have `_beh.tsv`

```shell (git)smaug:/mnt/btrfs/datasets/datalad/crawl/openneuro[master]git $> for ds in ds*; do f=$(find $ds -iname *_beh.tsv | head -n 1); [ -z "$f" ] && continue; echo "$ds $f"; done ds000113 ds000113/sub-22/beh/sub-22_task-movie_beh.tsv ds001454 ds001454/sub-01/ses-1/beh/sub-01_ses-1_task-test_beh.tsv ds001784 ds001784/sub-01/beh/sub-01_task-afmsit_acq-dbsoff_beh.tsv ds002778 ds002778/sub-hc1/ses-hc/beh/sub-hc1_ses-hc_task-rest_beh.tsv ds003696 ds003696/derivatives/preproc-DPABI/sub-101/ses-01/func/sub-101_ses-01_task-affordance_run-1_desc-DPABI_beh.tsv ds003751 ds003751/sub-mit003/beh/sub-mit003_task-Emotion_beh.tsv ds003766 ds003766/sub-001/beh/sub-001_task-foodchoice_beh.tsv ds003823 ds003823/sub-5001/beh/sub-5001_task-recall_beh.tsv ds003838 ds003838/sub-013/beh/sub-013_task-memory_beh.tsv ds004085 ds004085/sub-1/beh/sub-1_task-SlowFast_beh.tsv ds004094 ds004094/sub-100/beh/sub-100_task-group_beh.tsv ds004147 ds004147/sub-27/beh/sub-27_task-casinos_beh.tsv ds004152 ds004152/sub-01/beh/sub-01_task-drumtrainer_beh.tsv ds004200 ds004200/sub-01/beh/sub-01_task-temporalscaling_beh.tsv ds004256 ds004256/sub-001/beh/sub-001_task-deviantdetection_beh.tsv ds004262 ds004262/sub-01/beh/sub-01_task-gnomes_beh.tsv ds004264 ds004264/sub-01/beh/sub-01_task-steertheship_beh.tsv ds004276 ds004276/sub-001/beh/sub-001_task-words_beh.tsv ds004286 ds004286/sub-01/ses-01/beh/sub-01_ses-01_task-videofeatures_beh.tsv ds004395 ds004395/sub-LTP063/ses-0/beh/sub-LTP063_ses-0_task-ltpFR_beh.tsv ds004473 ds004473/sub-1/beh/sub-1_task-SlowFast_beh.tsv ds004511 ds004511/sub-S200116/ses-01/beh/sub-S200116_ses-01_task-GG_run-01_beh.tsv ds004574 ds004574/sub-001/beh/sub-001_task-Oddball_beh.tsv ds004580 ds004580/sub-001/beh/sub-001_task-Simon_beh.tsv ds004706 ds004706/sub-LTP448/ses-0/beh/sub-LTP448_ses-0_task-NiclsCourierClosedLoop_beh.tsv ds004724 ds004724/sub-20950/beh/sub-20950_task-StopSignal_beh.tsv ds004789 ds004789/sub-R1076D/ses-0/beh/sub-R1076D_ses-0_task-FR1_beh.tsv ds004809 ds004809/sub-R1093J/ses-0/beh/sub-R1093J_ses-0_task-catFR1_beh.tsv ds004865 ds004865/sub-TJ001/ses-0/beh/sub-TJ001_ses-0_task-pyFR_beh.tsv ds004902 ds004902/sub-01/ses-2/beh/sub-01_ses-2_task-pvt_beh.tsv ```