chore: remove class data-files-btn

This class is assigned to buttons that:
- **either** have Bootstrap btn-primary
    (in which case the `.workbench-content .btn-primary` styles it)
- **or** are our custom `<Button>`
    (in which case the `composes: c-button` styles it)

client/src/components/DataFiles/DataFilesModals/DataFilesModalTables/DataFilesModalListingTable.jsx

@@ -120,7 +120,7 @@ const DataFilesModalButtonCell = ({
       <span>
         <Button
           type="primary"
-          className="float-right data-files-btn"
+          className="float-right"
           disabled={disabled}
           onClick={onClick}
         >

client/src/components/DataFiles/DataFilesProjectMembers/_cells/ProjectRoleSelector.jsx

@@ -75,7 +75,6 @@ const ProjectRoleSelector = ({ projectId, username }) => {
       {data.role !== selectedRole && !isFetching && (
         <Button
           type="primary"
-          className="data-files-btn"
           onClick={() =>
             setProjectRole({ oldRole: data.role, newRole: selectedRole })
           }

client/src/components/DataFiles/DataFilesSidebar/DataFilesSidebar.jsx

@@ -72,7 +72,6 @@ const DataFilesAddButton = ({ readOnly }) => {
         <DropdownToggle
           color="primary"
           id="data-files-add"
-          className="data-files-btn"
         >
           + Add
         </DropdownToggle>

client/src/components/DataFiles/DataFilesSidebar/DataFilesSidebar.scss

@@ -1,14 +1,5 @@
 @import '../../../styles/components/dropdown-menu.css';
 
-.data-files-btn {
-  background-color: var(--global-color-accent--normal);
-  border-color: var(--global-color-accent--normal);
-  border-radius: 0;
-}
-
-.data-files-btn-cancel {
-  border-radius: 0;
-}
 
 #add-button-wrapper {
   padding-left: var(--horizontal-buffer);