highlighter: Remove EmptyDef since it's superseeded by a nil check of SyntaxDef

internal/buffer/buffer.go

@@ -908,8 +908,6 @@ func (b *Buffer) UpdateRules() {
 		if b.SyntaxDef != nil {
 			b.Settings["filetype"] = b.SyntaxDef.FileType
 		}
-	} else {
-		b.SyntaxDef = &highlight.EmptyDef
 	}
 
 	if b.SyntaxDef != nil {

pkg/highlight/highlighter.go

@@ -67,9 +67,6 @@ func combineLineMatch(src, dst LineMatch) LineMatch {
 // A State represents the region at the end of a line
 type State *region
 
-// EmptyDef is an empty definition.
-var EmptyDef = Def{nil, &rules{}}
-
 // LineStates is an interface for a buffer-like object which can also store the states and matches for every line
 type LineStates interface {
 	LineBytes(n int) []byte