svm: Delete unused svm_get_unmapped_area ops

ascend inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4UR5Y


CVE: NA

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svm_get_unmapped_area will be no longer used.

Signed-off-by: Lijun Fang <fanglijun3@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>