Update legacy-reset variables for BS v4.0.0

Author: thallada

sass/_legacy-reset.scss

@@ -6,7 +6,7 @@
 // To use, include this reset before all other Bootstrap references
 // within the consuming application or package's pipeline.
 
-@import "~bootstrap/scss/bootstrap-reboot";
+@import "~bootstrap/scss/reboot";
 @import "edx/_theme";
 
 // The Open edX platform's legacy base font size is 62.5%. This
@@ -43,21 +43,18 @@ $input-btn-padding-y-sm: $input-btn-padding-y-sm / $base-rem-size;
 $input-btn-padding-x-lg: $input-btn-padding-x-lg / $base-rem-size;
 $input-btn-padding-y-lg: $input-btn-padding-y-lg / $base-rem-size;
 $form-text-margin-top: $form-text-margin-top / $base-rem-size;
-$form-check-margin-bottom: $form-check-margin-bottom / $base-rem-size;
 $form-check-input-gutter: $form-check-input-gutter / $base-rem-size;
 $form-check-input-margin-y: $form-check-input-margin-y / $base-rem-size;
 $form-check-input-margin-x: $form-check-input-margin-x / $base-rem-size;
 $form-check-inline-margin-x: $form-check-inline-margin-x / $base-rem-size;
 $custom-control-gutter: $custom-control-gutter / $base-rem-size;
 $custom-control-spacer-x: $custom-control-spacer-x / $base-rem-size;
-$custom-control-spacer-y: $custom-control-spacer-y / $base-rem-size;
 $custom-control-indicator-size: $custom-control-indicator-size / $base-rem-size;
 $custom-control-indicator-box-shadow: $custom-control-indicator-box-shadow / $base-rem-size;
 $custom-select-padding-x: $custom-select-padding-x / $base-rem-size;
 $custom-select-padding-y: $custom-select-padding-y / $base-rem-size;
 $custom-select-indicator-padding: $custom-select-indicator-padding / $base-rem-size;
 $custom-file-height: $custom-file-height / $base-rem-size;
-$custom-file-width: $custom-file-width / $base-rem-size;
 $custom-file-focus-box-shadow: $custom-file-focus-box-shadow / $base-rem-size;
 $custom-file-padding-x: $custom-file-padding-x / $base-rem-size;
 $custom-file-padding-y: $custom-file-padding-y / $base-rem-size;
@@ -94,5 +91,5 @@ $thumbnail-padding: $thumbnail-padding / $base-rem-size;
 $breadcrumb-padding-y: $breadcrumb-padding-y / $base-rem-size;
 $breadcrumb-padding-x: $breadcrumb-padding-x / $base-rem-size;
 $breadcrumb-item-padding: $breadcrumb-item-padding / $base-rem-size;
-$code-padding-x: $code-padding-x / $base-rem-size;
-$code-padding-y: $code-padding-y / $base-rem-size;
+$kbd-padding-x: $code-padding-x / $base-rem-size;
+$kbd-padding-y: $code-padding-y / $base-rem-size;