Remove edit-clear icon since it's in oxygen-icons.

icons/CMakeLists.txt

 include(ECMInstallIcons)
 ecm_install_icons( ICONS
   16-actions-cards-block.png        22-actions-lesson-remove.png      32-actions-practice-start.png
-  16-actions-edit-clear.png         22-actions-list-add-card.png      32-actions-practice-stop.png
+  22-actions-list-add-card.png      32-actions-practice-stop.png
   16-actions-edit-entry.png         22-actions-list-remove-card.png   32-actions-remove-duplicates.png
   16-actions-edit-table-row.png     22-actions-multiple-choice.png    32-actions-set-language.png
   16-actions-lesson-add.png         22-actions-practice-setup.png     32-actions-specific-setup.png
   16-actions-lesson-remove.png      22-actions-practice-start.png     48-actions-cards-block.png
-  16-actions-list-add-card.png      22-actions-practice-stop.png      48-actions-edit-clear.png
+  16-actions-list-add-card.png      22-actions-practice-stop.png      
   16-actions-list-remove-card.png   22-actions-remove-duplicates.png  48-actions-edit-entry.png
   16-actions-multiple-choice.png    22-actions-set-language.png       48-actions-edit-table-row.png
   16-actions-practice-setup.png     22-actions-specific-setup.png     48-actions-lesson-add.png
   16-actions-practice-start.png     32-actions-cards-block.png        48-actions-lesson-remove.png
-  16-actions-practice-stop.png      32-actions-edit-clear.png         48-actions-list-add-card.png
+  16-actions-practice-stop.png      48-actions-list-add-card.png
   16-actions-remove-duplicates.png  32-actions-edit-entry.png         48-actions-list-remove-card.png
   16-actions-set-language.png       32-actions-edit-table-row.png     48-actions-multiple-choice.png
   16-actions-specific-setup.png     32-actions-lesson-add.png         48-actions-practice-setup.png
   22-actions-cards-block.png        32-actions-lesson-remove.png      48-actions-practice-start.png
-  22-actions-edit-clear.png         32-actions-list-add-card.png      48-actions-practice-stop.png
+  32-actions-list-add-card.png      48-actions-practice-stop.png
   22-actions-edit-entry.png         32-actions-list-remove-card.png   48-actions-remove-duplicates.png
   22-actions-edit-table-row.png     32-actions-multiple-choice.png    48-actions-set-language.png
   22-actions-lesson-add.png         32-actions-practice-setup.png     48-actions-specific-setup.png
 
   sc-actions-cards-block.svgz     sc-actions-lesson-remove.svgz     sc-actions-remove-duplicates.svgz
-  sc-actions-edit-clear.svgz      sc-actions-list-add-card.svgz     sc-actions-set-language.svgz
+  sc-actions-list-add-card.svgz   sc-actions-set-language.svgz
   sc-actions-edit-entry.svgz      sc-actions-list-remove-card.svgz  sc-actions-specific-setup.svgz
   sc-actions-edit-table-row.svgz  sc-actions-practice-setup.svgz
   sc-actions-lesson-add.svgz      sc-actions-practice-start.svgz