Remove button variant class when no variant set (#3372)

src/components/button/_macro.njk

@@ -72,7 +72,7 @@
     {% else %}
         type="{{ buttonType }}"
     {% endif %}
-    class="ons-btn{{ ' ' + params.classes if params.classes else '' }}{% if params.variants and params.variants is not string %}{% for variant in params.variants %}{{ ' ' }}ons-btn--{{ variant }}{% endfor %}{% else %}{{ ' ' }}ons-btn--{{ params.variants }}{% endif %}{{ ' ons-btn--link ons-js-submit-btn' if params.url }}{{ variantClasses }}"
+    class="ons-btn{{ ' ' + params.classes if params.classes else '' }}{% if params.variants and params.variants is not string %}{% for variant in params.variants %}{{ ' ' }}ons-btn--{{ variant }}{% endfor %}{% elif params.variants %}{{ ' ' }}ons-btn--{{ params.variants }}{% endif %}{{ ' ons-btn--link ons-js-submit-btn' if params.url }}{{ variantClasses }}"
     {% if params.id %}id="{{ params.id }}"{% endif %}
     {% if params.value and tag != "a" %}value="{{ params.value }}"{% endif %}
     {% if params.name and tag != "a" %}name="{{ params.name }}"{% endif %}