themes: Remove the brief top bar tooltips

These are the tooltips of the images. Mousing over the figures next to
the images shows a more verbose tooltip.

For #1068/#1060

data/themes/default.cfg

@@ -175,7 +175,7 @@
         [label]
             id=gold-icon
             icon=themes/gold.png
-            text= _ "gold"
+            text= ""
             ref=gold-box-center
             rect="=+1,=-1,+17,+17"
             xanchor=fixed
@@ -184,7 +184,7 @@
         [label]
             id=villages-icon
             icon=themes/villages.png
-            text= _ "villages"
+            text= ""
             ref=villages-box-center
             rect="=+1,=-1,+17,+17"
             xanchor=fixed
@@ -193,7 +193,7 @@
         [label]
             id=units-icon
             icon=themes/units.png
-            text= _ "units"
+            text= ""
             ref=units-box-center
             rect="=+1,=-1,+17,+17"
             xanchor=fixed
@@ -202,7 +202,7 @@
         [label]
             id=upkeep-icon
             icon=themes/upkeep.png
-            text= _ "upkeep"
+            text= ""
             ref=upkeep-box-center
             rect="=+1,=-1,+25,+17"
             xanchor=fixed
@@ -211,7 +211,7 @@
         [label]
             id=income-icon
             icon=themes/income.png
-            text= _ "income"
+            text= ""
             ref=income-box-center
             rect="=+1,=-1,+25,+17"
             xanchor=fixed