Remove max-width from perseus editor problemarea

Summary:
The forcibly setting 480px on the content instead of 100% seems
to have obliviated the need for max width even on the table-cell.

Test Plan:
Make a too-big table inside perseus:
http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22%5Cn%5Cnheader%201%20%7C%20header%202%20%7C%20header%203%5Cn-%20%7C%20-%20%7C%20-%5Cndata%201%20%7C%20daadsffdafdafadfadsfajhdafkjhdafkjdfsahkjfdshdkfjashadfkjdfhkajdfshfkdjashdfakjhdfkjadfshdkafjhadfkjdfashdkfjsa%7C%20data%203%5Cndata%204%20%7C%20data%205%20%7C%20data%206%5Cndata%207%20%7C%20data%208%20%7C%20data%209%22%2C%22widgets%22%3A%7B%7D%7D%2C%22answerArea%22%3A%7B%22type%22%3A%22multiple%22%2C%22options%22%3A%7B%22content%22%3A%22%22%2C%22widgets%22%3A%7B%7D%7D%2C%22calculator%22%3Afalse%7D%2C%22hints%22%3A%5B%5D%7D

Auditors: alpert