Remove support for backticks from the grammar and compiler.

Still need to remove traces of the UNARY_CONVERT opcode.
diff --git a/Lib/tokenize.py b/Lib/tokenize.py
index 27d566a..5d65267 100644
--- a/Lib/tokenize.py
+++ b/Lib/tokenize.py
@@ -83,7 +83,7 @@
                  r"~")
 
 Bracket = '[][(){}]'
-Special = group(r'\r?\n', r'[:;.,`@]')
+Special = group(r'\r?\n', r'[:;.,@]')
 Funny = group(Operator, Bracket, Special)
 
 PlainToken = group(Number, Funny, String, Name)