gitk: eliminate Interface color option from gui

gitk offers to change the ui color on the colors prefs page, but the
variable set has no effect because gitk is using themes. Let's eliminate
the "Interface" color selection option from that page.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>

Author: mark987

gitk

@@ -11741,10 +11741,6 @@ proc prefspage_colors {notebook} {
 
     ttk::label $page.cdisp -text [mc "Colors: press to choose"] -font mainfontbold
     grid $page.cdisp - -sticky w -pady 10
-    label $page.ui -padx 40 -relief sunk -background $uicolor
-    ttk::button $page.uibut -text [mc "Interface"] \
-       -command [list choosecolor uicolor {} $page [mc "interface"]]
-    grid x $page.uibut $page.ui -sticky w
     label $page.bg -padx 40 -relief sunk -background $bgcolor
     ttk::button $page.bgbut -text [mc "Background"] \
         -command [list choosecolor bgcolor {} $page [mc "background"]]
@@ -11788,7 +11784,6 @@ proc prefspage_set_colorswatches {page} {
     global uicolor bgcolor fgcolor ctext diffcolors selectbgcolor markbgcolor
     global diffbgcolors
 
-    $page.ui configure -background $uicolor
     $page.bg configure -background $bgcolor
     $page.fg configure -background $fgcolor
     $page.diffold configure -background [lindex $diffcolors 0]