Following the C to Go translation, some useless variables
were left in the code. In fmt.go, this was harmless.
In lex.go, it broke the error message related to
non-canonical import paths.

Fix it, and remove the useless variables.

The added test case is ignored in the go/types tests, since
the behavior of the non-canonical import path check seems
to be different.

Fixes #11362

Change-Id: Ic9129139ede90357dc79ebf167af638cf44536fa
Reviewed-on: https://go-review.googlesource.com/15580Reviewed-by: Marvin Stenger <marvin.stenger94@gmail.com>
Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>