efs: clean up -Wunused-const-variable= warning

When building with W=1, the following warning occurs.

In file included from fs/efs/super.c:18:0:
fs/efs/efs.h:22:19: warning: `cprt' defined but not used [-Wunused-const-variable=]
 static const char cprt[] = "EFS: "EFS_VERSION" - (c) 1999 Al Smith
<Al.Smith@aeschi.ch.eu.org>";
                   ^~~~
The 'cprt' is not used in any files, we move the copyright statement
into the comment.

Link: https://lkml.kernel.org/r/20230803015103.192985-1-wangzhu9@huawei.com


Signed-off-by: Zhu Wang <wangzhu9@huawei.com>
Cc: Al Smith <Al.Smith@aeschi.ch.eu.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>