term: remove unused variable

The eraseUnderCursor variable is unused, it came in with the import
of the x/crypto/ssh/terminal package at d7a7210 but is not referenced
here.

When this package is vendored, the unused unexported name trips warnings
from tools like staticcheck.

Change-Id: I4289239edcdfec434ec26b164ae6c0a9b9ee7067
GitHub-Last-Rev: a4ab5868b4
GitHub-Pull-Request: golang/term#10
Reviewed-on: https://go-review.googlesource.com/c/term/+/446455
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

terminal.go

@@ -233,7 +233,6 @@ func (t *Terminal) queue(data []rune) {
 	t.outBuf = append(t.outBuf, []byte(string(data))...)
 }
 
-var eraseUnderCursor = []rune{' ', keyEscape, '[', 'D'}
 var space = []rune{' '}
 
 func isPrintable(key rune) bool {