Fixed size of buttons in branches list

Closes #18677

app/views/projects/branches/_branch.html.haml

@@ -20,15 +20,15 @@
         protected
     .controls.hidden-xs
       - if create_mr_button?(@repository.root_ref, branch.name)
-        = link_to create_mr_path(@repository.root_ref, branch.name), class: 'btn btn-grouped btn-xs' do
+        = link_to create_mr_path(@repository.root_ref, branch.name), class: 'btn btn-default' do
           Merge Request
 
       - if branch.name != @repository.root_ref
-        = link_to namespace_project_compare_index_path(@project.namespace, @project, from: @repository.root_ref, to: branch.name), class: 'btn btn-grouped btn-xs', method: :post, title: "Compare" do
+        = link_to namespace_project_compare_index_path(@project.namespace, @project, from: @repository.root_ref, to: branch.name), class: 'btn btn-default', method: :post, title: "Compare" do
           Compare
 
       - if can_remove_branch?(@project, branch.name)
-        = link_to namespace_project_branch_path(@project.namespace, @project, branch.name), class: 'btn btn-grouped btn-xs btn-remove remove-row has-tooltip', title: "Delete branch", method: :delete, data: { confirm: "Deleting the '#{branch.name}' branch cannot be undone. Are you sure?", container: 'body' }, remote: true do
+        = link_to namespace_project_branch_path(@project.namespace, @project, branch.name), class: 'btn btn-remove remove-row has-tooltip', title: "Delete branch", method: :delete, data: { confirm: "Deleting the '#{branch.name}' branch cannot be undone. Are you sure?", container: 'body' }, remote: true do
           = icon("trash-o")
 
     - if branch.name != @repository.root_ref