Remove noneed plotting code

• remove ax.linkedX because there is no use for it.
• remove zoom_marker2_follow_mouse: we don't let zoom_marker2 to follow mouse anymore because it slow down the performance but have the zoom_marker2 to show up for short time the perform zoom.

assigned to @ldam and @kienle

unassigned @kienle

requested review from @kienle

added 3 commits

• 731f673e...8c498265 - 2 commits from branch master
• 2b5f423e - Merge branch 'master' into remove-noneed_plotting_code

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merged

mentioned in commit 283b6b92