Remove comment about gitignore for BUILD files.

Change-Id: Ic1c795d9d961b309d269b1bc4bccb7522f288e9b
Rationale: we haven't modified any gitignore file. lberki has a new proposal to steer this in a new direction, so let's reflect the comment to the current reality.
diff --git a/bp2build/constants.go b/bp2build/constants.go
index 23bca83..70f320e 100644
--- a/bp2build/constants.go
+++ b/bp2build/constants.go
@@ -18,7 +18,7 @@
 	// When both a BUILD and BUILD.bazel file are exist in the same package, the BUILD.bazel file will
 	// be preferred for use within a Bazel build.
 
-	// The file name used for automatically generated files. Files with this name are ignored by git.
+	// The file name used for automatically generated files.
 	GeneratedBuildFileName = "BUILD"
 	// The file name used for hand-crafted build targets.
 	HandcraftedBuildFileName = "BUILD.bazel"