.gitignore: roll back ".gitignore: ignore emacs backup files"

The .gitignore file should only list files created by the build.

Change-Id: I0cab4662e54a560851cf5d9c4b4d18c4eb9a6bb6
Reviewed-on: https://go-review.googlesource.com/93437
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/.gitignore b/.gitignore
index f6ca776..5a9d62e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,2 @@
 # Add no patterns to .gitignore except for files generated by the build.
 last-change
-*~