Use ‘exclude list’ instead of ‘blacklist’ (#4297)

This replaces all uses of ‘blacklist’ with ‘exclude list’. Benefits:

- It is racially neutral terminology; see e.g. [1]

- It makes the meaning more clear. In fact, with the popular Python
  autoformatter called ‘black’, also used by this project, files can be
  ‘blackened’ which is something completely different from them being on
  a blacklist.

[1] https://chromium.googlesource.com/chromium/src/+/master/styleguide/inclusive_code.md#racially-neutral

tests/pytype_test.py

@@ -4,7 +4,7 @@
 Depends on pytype being installed.
 
 If pytype is installed:
-    1. For every pyi, do nothing if it is in pytype_blacklist.txt.
+    1. For every pyi, do nothing if it is in pytype_exclude_list.txt.
     2. Otherwise, call 'pytype.io.parse_pyi'.
 Option two will load the file and all the builtins, typeshed dependencies. This
 will also discover incorrect usage of imported modules.
@@ -72,8 +72,8 @@ class PathMatcher:
         return self.matcher.search(path)
 
 
-def load_blacklist(typeshed_location: str) -> List[str]:
-    filename = os.path.join(typeshed_location, "tests", "pytype_blacklist.txt")
+def load_exclude_list(typeshed_location: str) -> List[str]:
+    filename = os.path.join(typeshed_location, "tests", "pytype_exclude_list.txt")
     skip_re = re.compile(r"^\s*([^\s#]+)\s*(?:#.*)?$")
     skip = []
 
@@ -159,10 +159,10 @@ def check_python_exes_runnable(*, python27_exe_arg: str, python36_exe_arg: str)
 
 
 def determine_files_to_test(*, typeshed_location: str, paths: Sequence[str]) -> List[Tuple[str, int]]:
-    """Determine all files to test, checking if it's in the blacklist and which Python versions to use.
+    """Determine all files to test, checking if it's in the exclude list and which Python versions to use.
 
     Returns a list of pairs of the file path and Python version as an int."""
-    skipped = PathMatcher(load_blacklist(typeshed_location))
+    skipped = PathMatcher(load_exclude_list(typeshed_location))
     filenames = find_stubs_in_paths(paths)
     files = []
     for f in sorted(filenames):