[BUGFIX] Remove additional button classes from dropdown items

When using a <button> in a bootsrap dropdown
menu, additional button classes, such as ".btn"
are not necessary, but might lead to display errors.

Those classes are therefore now removed.

Resolves: #97909
Releases: main
Change-Id: I1c3ef81dce52e31d15a3d93c1e215f033b22a4a1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75130


Tested-by: core-ci <typo3@b13.com>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>