Cleanup findnocoding.py and pysource.py scripts (with infile/infile.close)

Tools/scripts/findnocoding.py

@@ -60,7 +60,6 @@ def needs_declaration(fullpath):
 
         if get_declaration(line1) or get_declaration(line2):
             # the file does have an encoding declaration, so trust it
-            infile.close()
             return False
 
         # check the whole file for non utf-8 characters

Tools/scripts/pysource.py

@@ -55,8 +55,8 @@ def looks_like_python(fullpath):
     if infile is None:
         return False
 
-    line = infile.readline()
-    infile.close()
+    with infile:
+        line = infile.readline()
 
     if binary_re.search(line):
         # file appears to be binary
@@ -76,8 +76,8 @@ def can_be_compiled(fullpath):
     if infile is None:
         return False
 
-    code = infile.read()
-    infile.close()
+    with infile:
+        code = infile.read()
 
     try:
         compile(code, fullpath, "exec")