Revert "Add COPYING symlink, to help gitlab and go-license-detector."

This reverts commit e7eacd6bdc79868f239c3ee5e665b08c8ec280a5.

The symlink didn't help, and it is somewhat misleading.

diff --git a/COPYING b/COPYING
deleted file mode 120000 (symlink)
index 6aac817..0000000
--- a/COPYING
+++ /dev/null
@@ -1 +0,0 @@
-COPYING.LESSERv3
\ No newline at end of file