jest: remove unused snapshot

app/soapbox/components/__tests__/__snapshots__/column_back_button_slim-test.js.snap

@@ -1,22 +0,0 @@
-// Jest Snapshot v1, https://goo.gl/fbAQLP
-
-exports[`<ColumnBackButtonSlim /> renders correctly 1`] = `
-<div
-  className="column-back-button--slim"
->
-  <div
-    className="column-back-button column-back-button--slim-button"
-    onClick={[Function]}
-    onKeyUp={[Function]}
-    role="button"
-    tabIndex="0"
-  >
-    <i
-      alt="chevron-left"
-      className="fa fa-chevron-left column-back-button__icon fa-fw"
-      role="img"
-    />
-    Back
-  </div>
-</div>
-`;