Update gitignore.

.gitignore

@@ -33,7 +33,6 @@
 /tests/debugging/archive/
 /tests/*.c
 /tests/*.cpp
-/tools/_build/
 /website/docs/
 *.vcxproj.user
 .vs/
@@ -47,8 +46,4 @@
 /research/ma_atomic.c
 /research/miniaudio_engine.c
 /tests/stress/
-/tools/codegen/miniaudio_amalgamator.c
-/tools/codegen/miniaudio_codegen_utils.c
-/tools/codegen/miniaudio_docgen.c
-/tools/codegen/miniaudio_hrtfgen.c
-/tools/codegen/miniaudio_splitter.c
+/tools/hrtfgen/