Setup And Upgrade :: Clarification On Non-integer Constants Are Not Allowed In ORDER BY Clause In 90

We're upgrading our SQL Server database from 2005 to 2012.I ran the Upgrade Advisory report and got this issue "Non-integer constants are not allowed in the ORDER BY clause in 90" because of the script below

SELECT
gp.BRAND+' <> '+gp.CATEGORY AS 'full name',
gp.PRODCODE,
gp.CATEGORY
FROM dbo.GFK_PRODUCT gp
ORDER BY
'full name'

I tried running the same query in our test SQL Server 2012 and it ran successfully. Now I'm confuse if i still need to change it.I google the issue a bit and came across this link and mentioned this.

1.) Non-integer constants are ... constants that are not integer number.

Example: 'string1' represents
a string constant
0x01 represents
a varbinary constant
{ts
'2015-02-26 06:00:00'} represents a datetime constant

1.23 represents
a numeric constants

2) So single quotes are used to define a string constants / character string constants but SQL Server allows also to use single quotation marks use also as column identifier
delimiter:
SELECT ... expression AS 'Column1'
FROM ...

In this context is clear that 'Column1' is a column identifier but when used in ORDER BY : ORDER BY 'Column1' it generates confusion because SQL Server doesn't knows if it represents a string literal (character string constant) or it represents a column identifier / column name."Do I still need to change the existing code even though it's working fine in 2012? If yes, it is because of best practice reason or it will total get deprecated/not working in the future version?