Correcting path to a file

PR 1822 moved this file into langapi, updated the comment (and removed
the erroneous s at the end of the file name).

Author: thk123

src/goto-programs/lazy_goto_functions_map.h

@@ -18,7 +18,7 @@
 /// access to goto programs while they are still under construction.
 /// The intended workflow:
 /// 1. The front-end registers the functions that are potentially
-///   available, probably by use of util/language_files.h
+///   available, probably by use of langapi/language_file.h
 /// 2. The main function registers functions that should be run on
 ///   each program, in sequence, after it is converted.
 /// 3. Analyses will then access functions using the `at` function