PEP 205, 611: Fix word duplications and grammar

pep-0205.txt

@@ -335,7 +335,7 @@ handle on an object that does not increment the object's reference
 count.  This means that holding a vref on an object will not keep
 the object from being destroyed.  This would allow the Python
 programmer, for example, to create the aforementioned tree
-structure tree structure, which is automatically destroyed when it
+structure, which is automatically destroyed when it
 is no longer in use -- by making all of the parent back-references
 into vrefs, they no longer create reference cycles which keep the
 tree from being destroyed.

pep-0611.rst

@@ -38,7 +38,7 @@ It is unsafe as malicious or poorly generated code could cause values to exceed
 
 For example, line numbers are represented by 32 bit values internally. 
 This is inefficient, given that modules almost never exceed a few thousand lines.
-Despite being inefficient, is still vulnerable to overflow as
+Despite being inefficient, it is still vulnerable to overflow as
 it is easy for an attacker to created a module with billions of newline characters.
 
 Memory access is usually a limiting factor in the performance of modern CPUs.