Remove `tab-bar-echo-area` from list of indirectly covered packages

Hello Prot,

this is just a quick update of the docs of the Modus themes, and more specifically to the section "Indirectly covered packages" contained within them.

I have previously confirmed to you that all faces of the tab-bar-echo-area package inherit from basic faces only and to not add or require any extra styling. As of yesterday, this is no longer true: the tab-bar-echo-area-tab face now defines :inverse-video t. Unfortunately, I couldn't find a face that Emacs provides that I could inherit from here (menu comes close, but doesn't invert "the video" for x-toolkit environments (link)).

I believe that the tab-bar-echo-area-tab face would not need extra styling in the Modus themes with regards to accessibility as the inversion of video just swaps the fg/bg colors, but I'm definitely not an expert on the subject. The package's README has screenshots to illustrate.

Thank you!