Revert "gitattributes: Mark yarn.lock as "binary", i.e. suppress diffs."

This reverts commit a717ac6.

.gitattributes affects the behavior of many Git operations like rebase
and merge and mergetool, not just the output of show and diff.
Treating yarn.lock as binary was making it too hard to deal with
yarn.lock diffs when we actually needed them.  Also, the GitHub
website ignores this setting and suppresses large parts of diffs
regardless.

Signed-off-by: Anders Kaseorg <[email protected]>

Author: andersk

.gitattributes

@@ -11,4 +11,3 @@
 *.otf binary
 *.tif binary
 *.ogg binary
-yarn.lock binary