all_test: drop a trailing space gofmt flags

TestDBPageVtab's comment about -DSQLITE_ENABLE_DBPAGE_VTAB carried a trailing
space, which made all_test.go the one hand-written file in the tree that
gofmt -l reports. Comment text only; nothing else changes.

Noticed by Ian Chechin while preparing GitLab merge request #135, which does
not touch this file.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>