WebView: fix setSafeBrowsingWhitelist table in docs

No change to logic, only docs changes.

The documentation for setSafeBrowsingWhitelist uses a table to describe
whitelist rules. However, this table was previously formatted
incorrectly (it uses <th> elements for each cell, when normal data cells
should use <td> according to Android API guidelines).

This fixes the table to conform to the guidelines, adjusts white space
for consistency, and removes an unnecessary <p> element.

Bug: 65173825
Test: make docs (and manually verify the table looks correct)
Change-Id: I5d7390a44613aaa3acb147a69f8e0ce741e817ed