Further polish SQLite vendoring

- Now integrated with `make tags` for Emacs IDE features
- Delete some old deprecated broken full-text search engines
- Rename .h → .inc files that don't meet our definition of header
- Make sure every #include line is normal form so tools understand

See #162

third_party/sqlite3/sqliteicu.inc

@@ -0,0 +1,27 @@
+/*
+** 2008 May 26
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+******************************************************************************
+**
+** This header file is used by programs that want to link against the
+** ICU extension.  All it does is declare the sqlite3IcuInit() interface.
+*/
+#include "third_party/sqlite3/sqlite3.h"
+/* clang-format off */
+
+#ifdef __cplusplus
+extern "C" {
+#endif  /* __cplusplus */
+
+int sqlite3IcuInit(sqlite3 *db);
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif  /* __cplusplus */