LIKE is not a good choice here: it's generally used for strings, and a YEAR column should be an integer, not a string.
And LIKE is only really useful when you give it a wildcard specification, similar to "*.jpg" in Windows will return all JPEG files in a folder.
For MySQL and SQL Server, the primary wildcard is the '%' character which matches anything in the same ways the '*' dowes in Windows.
If you don't need wildcards, don't use LIKE; use '=' instead:
DELETE FROM poa WHERE year2 = 2017 AND proyecto = 'proy1';