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/main.c

@@ -14,17 +14,17 @@
 ** other files are for internal use by SQLite and should not be
 ** accessed by users of the library.
 */
-#include "third_party/sqlite3/sqliteInt.h"
+#include "third_party/sqlite3/sqliteInt.inc"
 /* clang-format off */
 
 #ifdef SQLITE_ENABLE_FTS3
-#include "third_party/sqlite3/fts3.h"
+#include "third_party/sqlite3/fts3.inc"
 #endif
 #ifdef SQLITE_ENABLE_RTREE
-#include "third_party/sqlite3/rtree.h"
+#include "third_party/sqlite3/rtree.inc"
 #endif
 #if defined(SQLITE_ENABLE_ICU) || defined(SQLITE_ENABLE_ICU_COLLATIONS)
-#include "third_party/sqlite3/sqliteicu.h"
+#include "third_party/sqlite3/sqliteicu.inc"
 #endif
 
 /*