Has Form.aCheckInForm been removed in 4.7?
I can't seem to find it.

Form.aUndoFormsCheckOut is still there

The proper way to check out is here.

http://community.k2.com/t5/K2-blackpearl/Unable-to-Checkin-Form/ta-p/82392

To help you by generating the query to executing according the form or view display name:

  
--Undo checkout for one form/view:    
--UndoCheckout:
DECLARE @DisplayNameToFound  nvarchar(100)
SET @DisplayNameToFound='CurrentTickets'   --FILL HERE THE FORM OR VIEW DISPLAY NAME


--Check first on the view:
DECLARE @FormOrViewId  nvarchar(100)
SET @FormOrViewId = (SELECT  View].ID FROM  Form]..View] WHERE  View].DisplayName = @DisplayNameToFound)

IF @FormOrViewId IS NULL BEGIN
SET @FormOrViewId = ( SELECT  Form].ID FROM  Form]..Form] WHERE  Form].DisplayName = @DisplayNameToFound)
END

SELECT 'Form found: ''' + DisplayName + ''' Version: '+ convert( varchar,  Form].Version) AS 'Information' FROM  Form]..Form] WHERE Id=@FormOrViewId
UNION
SELECT 'CheckedOutBy:' + ISNULL((Form].CheckedOutBy,'WARNING: Seems to be not checked out!' ) FROM  Form]..Form] WHERE Id=@FormOrViewId
UNION
SELECT 'View found: ''' + DisplayName + ''' Version: '+ convert( varchar,  View].Version) FROM  Form]..View] WHERE Id=@FormOrViewId
UNION
SELECT 'CheckedOutBy:' + ISNULL((View].CheckedOutBy,'WARNING: Seems to be not checked out!' ) AS 'Information' FROM  Form]..View] WHERE Id=@FormOrViewId
ORDER BY 1 DESC

--Proposition of StatementToExecute:
SELECT 'declare @return_value int' + char(13) + char(10) + 
'exec @return_value =  Form]..aUndoFormsCheckOut] ' + char(13) + char(10) +
'@UserID = ''BY SQL - Original:' + ISNULL(CheckedOutBy, (select CheckedOutBy from  Form]..Form_Design]
WHERE  Form_Design].ID==Form].ID) + ' Only on Form_Design)')
 + ''', ' + char(13) + char(10) + --UserId is to used only for logs (procedure eLogMessage: table  AuditLog])
'@IDs = '''+@FormOrViewId +''', ' + char(13) + char(10) +
'@ClientStack = null' + char(13) + char(10) + char(13) + char(10) +
'select * from  Form]..AuditLog] order by 1 desc ' + char(13) + char(10) + char(13) + char(10) +
'--For corresponding Form :'+ char(13) + char(10) +
'select TOP 50 * from  Form]..AuditLog] WHERE Data='''+@FormOrViewId +''' order by 1 desc ' AS "Advised Statement" FROM  Form]..Form] WHERE Id=@FormOrViewId
UNION
SELECT 'declare @return_value int' + char(13) + char(10) + 
'exec @return_value =  Form]..aUndoViewsCheckOut] ' + char(13) + char(10) +
'@UserID = ''BY SQL - Original:' + ISNULL(CheckedOutBy, (select CheckedOutBy from  Form]..View_Design]
WHERE  View_Design].ID==View].ID) + ' Only on View_Design)')
 + ''', ' + char(13) + char(10) + --UserId is to used only for logs (procedure eLogMessage: table  AuditLog])
'@IDs = '''+@FormOrViewId +''', ' + char(13) + char(10) +
'@ClientStack = null' + char(13) + char(10) + char(13) + char(10) +
'select * from  Form]..AuditLog] order by 1 desc '+ char(13) + char(10) + char(13) + char(10) +
'--For corresponding view :'+ char(13) + char(10) +
'select TOP 50 * from  Form]..AuditLog] WHERE Data='''+@FormOrViewId +''' order by 1 desc ' AS "Advised Statement" FROM  Form]..View] WHERE Id=@FormOrViewId