Clean up miscellaneous metafiles (denoland#2981)

The yarn.lock file is moved from //third_party to the root of
the main repository. This is where other package metadata
files (e.g. Cargo.lock and package.json) are also located.

.gitattributes

@@ -6,5 +6,4 @@
 # This is relevant for Windows only, and requires git >= 2.19.2 to work.
 /core/libdeno/* symlink=dir
 /node_modules symlink=dir
-/tools/memory symlink=dir
 /website/* symlink=dir

.gitignore

@@ -1,18 +1,12 @@
-# build
+*.orig
+*.pyc
 *.swp
-/out/
+
+/.idea/
+/.vscode/
+/gclient_config.py_entries
+/gh-pages/
 /target/
-*.pyc
-gclient_config.py_entries
-yarn.lock
-# npm deps
-node_modules
-# editor files
-.idea
-.vscode
-# export dir for gh-pages
-/gh-pages
-# temp benchmark data
+/website/*.bundle.js
 /website/data.json
 /website/recent.json
-/website/*.bundle.js