exec: Remove redundant check in do_open_execat/uselib

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8LX53


CVE: NA

--------------------------------

There is a false positive WARNON happening in execve(2)/uselib(2)
syscalls with concurrent noexec-remount.

       execveat                           remount
do_open_execat(path/bin)
  do_filp_open
    path_openat
      do_open
        may_open
          path_noexec() // PASS
	                            remount(path->mnt, MS_NOEXEC)
WARNON(path_noexec(&file->f_path)) // path_noexec() checks fail

Since may_open() has already checked the same conditions, fix it by
removing 'S_ISREG' and 'path_noexec' check in do_open_execat()/uselib(2).

Fixes: 0fd338b2 ("exec: move path_noexec() check earlier")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>