Fix fontawesome4 less and some imperfection of #1119

[ttskch]

Already merged PR #1119 is not perfect in following points.

• In font-awesome4 directory, spinning.less is deleted but font-awesome.less still depends on spinning.less.
• In font-awesome directory, font-awesome.less no longer depends on spinning.less but spinning.less file still exists.

This PR fixes these. Thanks.