[sql] Stop building fts2.
Long ago, Chromium used fts2 for history full-text search. It was
later replaced by fts3, and even later that feature was deleted
entirely. fts2 is no longer used in the browser at all, so stop
compiling it.
Since SQLite is used by WebSQL, in theory this could affect web
authors, but WebSQL uses an authorizer to allow only specific virtual
table types. fts2 is not one of those types, I have verified manually
that fts2 tables cannot be created using WebSQL.
BUG=455817
Review URL: https://codereview.chromium.org/
999573003
Cr-Commit-Position: refs/heads/master@{#320135}