Don't truncate file before detecting language (#740)

Currently, we truncate a file's contents to 2048 bytes before passing it to
`go-enry`. I ran into a few cases where this is causing us to misclassify
files.

This PR removes the truncation. It should still be fine in terms of
performance, since `go-enry` is quite fast in general: ~1ms in my local
testing, even for large files. And we only run language detection if we plan to
index the file, which means we skip binary files and large files.

indexbuilder.go

@@ -397,12 +397,7 @@ func (b *IndexBuilder) addSymbols(symbols []*Symbol) {
 
 func DetermineLanguageIfUnknown(doc *Document) {
 	if doc.Language == "" {
-		c := doc.Content
-		// classifier is faster on small files without losing much accuracy
-		if len(c) > 2048 {
-			c = c[:2048]
-		}
-		doc.Language = enry.GetLanguage(doc.Name, c)
+		doc.Language = enry.GetLanguage(doc.Name, doc.Content)
 	}
 }