[REF] *: get rid of introduced @​extend

During first scss convertion, classes called as mixins were changed to
an @​extend instruction which was the best approximation given the fact
there is no equivalent in sass to do that. The problem is that the
instruction is slowing the scss computation a lot and might also break
the style in unexpected ways because of the complex unwanted selectors
the instruction induces.

This commit removes the need of extends. This is done case per case.
Sometimes this involves adding classes in xml, sometimes to change the
style a little, ... The button rendering refactoring which was made
at the start of the LESS to SASS merge was also done in prevision of
this.

After this commit, sass computation is like 5-6 times faster than less
computation while it was like 10 times *slower* before this commit.

1 files changed, 1 insertions, 1 deletions

diff --git a/addons/base_import/static/src/js/import_action.js b/addons/base_import/static/src/js/import_action.js
index 1e17798ae34..d995e9cf055 100644
--- a/addons/base_import/static/src/js/import_action.js
+++ b/addons/base_import/static/src/js/import_action.js
@@ -281,7 +281,7 @@ var DataImport = AbstractAction.extend(ControlPanelMixin, {
         // TODO: test that write // succeeded?
         this.$el.removeClass('oe_import_preview_error oe_import_error');
         this.$el.toggleClass(
-            'oe_import_noheaders',
+            'oe_import_noheaders text-muted',
             !this.$('input.oe_import_has_header').prop('checked'));
         this._rpc({
                 model: 'base_import.import',