eval: replace last uses of kr/pretty with format.Stmt
eval: replace last uses of kr/pretty with format.Stmt

A previous CL (a5c648c016) removed most uses of the
package github.com/kr/pretty but missed uses in
eval's tests.
Replace these last remnants with format.Stmt.
This will make fresh installs of go+ng faster.

neugram/ng,neugram/ng