remove 'sub_form' attribute that have accidentally been set on proxyfields.

see r17537 and http://www.erp5.org/UpgradeNote for details

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@17849 20353a03-c40f-0410-a6d1-a30d3c3de9de

bt5/erp5_accounting/bt/revision

-505
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+506
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bt5/erp5_crm/bt/revision

-123
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+124
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bt5/erp5_project/bt/revision

-370
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+371
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bt5/erp5_trade/bt/revision

-148
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+149
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product/ERP5/bootstrap/erp5_core/bt/revision

-591
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+592
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