draw: delete some dead code.
draw: delete some dead code.

Change-Id: I5830755b0be52df2be536a918f47684a1b7eda9d
Reviewed-on: https://go-review.googlesource.com/9232
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

golang/image