[IMP] hr_timesheet: remove separator when viewing task timesheets on mobile

[ksin-odoo]

The separator between the 'add timesheets' button and the total 'time spent' was visually distracting in mobile view. Removing it provides a cleaner interface.

task-5223266

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[robodoo]

[robodoo]

@xavierbol you may want to rebuild or fix this PR as it has failed CI.

[xavierbol]

robodoo r+