compress/flate: cancel redundant operations
compress/flate: cancel redundant operations

The assignment operation in the program seems to be redundant, the first judgment will continue to overwrite the previous value.
The subsequent slicing operation will cut all the values without frequency.

Change-Id: Id59fc36dd5bacfde881edaf0d9c1af5348286611
Reviewed-on: https://go-review.googlesource.com/c/go/+/244157
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Auto-Submit: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>
Reviewed-by: Joe Tsai <ad9e03fbec35106ba742f446a098eef3d5e31d20@google.com>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>

golang/go,nawawi/go,nawawi/go,nawawi/go,golang/go,nawawi/go,golang/go,nawawi/go,nawawi/go,nawawi/go,golang/go,golang/go,golang/go,golang/go,golang/go,nawawi/go