watchman: drop some py2 compat code

The `unicode` reference was being flagged by pytype, even though it was never
evaluated on py3.  There's more that can be dropped and `compat.py` can probably
be inlined if we don't care about minimizing the code changes from FB.  But I
don't feel like dealing with that.

hgext/fsmonitor/pywatchman/compat.py

@@ -32,37 +32,22 b' import sys'
 """Compatibility module across Python 2 and 3."""
 
 
-PYTHON2 = sys.version_info < (3, 0)
 PYTHON3 = sys.version_info >= (3, 0)
 
 # This is adapted from https://bitbucket.org/gutworth/six, and used under the
 # MIT license. See LICENSE for a full copyright notice.
-if PYTHON3:
-
-    def reraise(tp, value, tb=None):
-        try:
-            if value is None:
-                value = tp()
-            if value.__traceback__ is not tb:
-                raise value.with_traceback(tb)
-            raise value
-        finally:
-            value = None
-            tb = None
 
 
-else:
-    exec(
-        """
 def reraise(tp, value, tb=None):
     try:
-        raise tp, value, tb
+        if value is None:
+            value = tp()
+        if value.__traceback__ is not tb:
+            raise value.with_traceback(tb)
+        raise value
     finally:
+        value = None
         tb = None
-""".strip()
-    )
+
 
-if PYTHON3:
-    UNICODE = str
-else:
-    UNICODE = unicode  # noqa: F821 We handled versioning above
+UNICODE = str

hgext/fsmonitor/pywatchman/pybser.py

@@ -51,17 +51,15 b' BSER_TEMPLATE = b"\\x0b"'
 BSER_SKIP = b"\x0c"
 BSER_UTF8STRING = b"\x0d"
 
-if compat.PYTHON3:
-    STRING_TYPES = (str, bytes)
-    unicode = str
+STRING_TYPES = (str, bytes)
+unicode = str
+
 
-    def tobytes(i):
-        return str(i).encode("ascii")
+def tobytes(i):
+    return str(i).encode("ascii")
 
-    long = int
-else:
-    STRING_TYPES = (unicode, str)
-    tobytes = bytes
+
+long = int
 
 # Leave room for the serialization header, which includes
 # our overall length.  To make things simpler, we'll use an
@@ -87,7 +85,7 b' def _int_size(x):'
 def _buf_pos(buf, pos):
     ret = buf[pos]
     # Normalize the return type to bytes
-    if compat.PYTHON3 and not isinstance(ret, bytes):
+    if not isinstance(ret, bytes):
         ret = bytes((ret,))
     return ret
 
@@ -250,10 +248,7 b' class _bser_buffer:'
             else:
                 raise RuntimeError("Cannot represent this mapping value")
             self.wpos += needed
-            if compat.PYTHON3:
-                iteritems = val.items()
-            else:
-                iteritems = val.iteritems()  # noqa: B301 Checked version above
+            iteritems = val.items()
             for k, v in iteritems:
                 self.append_string(k)
                 self.append_recursive(v)