featureCompiler: simplify logic for MTI_FEATURES_PREFIX and os.path.sep

Lib/ufo2ft/featureCompiler.py

@@ -271,25 +271,13 @@ class MtiFeatureCompiler(BaseFeatureCompiler):
     fontTools.mtiLib.
     """
 
-    def __init__(self, ufo, ttFont=None, glyphSet=None, **kwargs):
-        super(MtiFeatureCompiler, self).__init__(
-            ufo, ttFont=ttFont, glyphSet=glyphSet, **kwargs
-        )
-        # defcon (as of 0.5.3) lists UFO data filenames using platform-specific
-        # path separators, whereas the new fontTools.ufoLib uses `fs` module
-        # internally which always requires UNIX forward slashes on all platforms
-        if hasattr(ufo, "reader") and hasattr(ufo.reader, "fs"):
-            sep = "/"
-        else:
-            sep = os.path.sep
-        self._mti_features_prefix = MTI_FEATURES_PREFIX + sep
-
     def setupFeatures(self):
         ufo = self.ufo
         features = {}
-        prefixLength = len(self._mti_features_prefix)
+        # includes the length of the "/" separator
+        prefixLength = len(MTI_FEATURES_PREFIX) + 1
         for fn in ufo.data.fileNames:
-            if fn.startswith(self._mti_features_prefix) and fn.endswith(".mti"):
+            if fn.startswith(MTI_FEATURES_PREFIX) and fn.endswith(".mti"):
                 content = tounicode(ufo.data[fn], encoding="utf-8")
                 features[fn[prefixLength:-4]] = content
         self.mtiFeatures = features