Clean doxygen_sqlite3.db

Generated by newer versions of Doxygen when built with sqlite3.
diff --git a/.gitignore b/.gitignore
index 7b7cf55..46e6325 100644
--- a/.gitignore
+++ b/.gitignore
@@ -55,6 +55,7 @@
 celt/tests/test_unit_mdct
 celt/tests/test_unit_rotation
 celt/tests/test_unit_types
+doc/doxygen_sqlite3.db
 doc/doxygen-build.stamp
 doc/html
 doc/latex
diff --git a/doc/Makefile.am b/doc/Makefile.am
index 296c4dd..31fddab 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -36,6 +36,7 @@
 	$(RM) -r latex
 	$(RM) -r man
 	$(RM) doxygen-build.stamp
+	$(RM) doxygen_sqlite3.db
 
 uninstall-local:
 	$(RM) -r $(DESTDIR)$(docdir)/html