fix: revert "copy the ruby version into rvm/gems (#790)" (#806)

This reverts commit 65d5ea4.

Author: aitkenster

run-build-functions.sh

@@ -336,7 +336,6 @@ install_dependencies() {
     echo "Started restoring cached ruby version"
     rm -rf $RVM_DIR/rubies/${fulldruby}
     cp -p -r $NETLIFY_CACHE_DIR/ruby_version/${fulldruby} $RVM_DIR/rubies/
-    cp -p -r $NETLIFY_CACHE_DIR/ruby_version/${fulldruby} $RVM_DIR/gems/
     echo "Finished restoring cached ruby version"
   fi