bpo-44257: fix "assigment_expr" typo + regenerate the grammar, and remove unused imports (GH-29393)

Co-authored-by: Wim Glenn <wglenn@jumptrading.com>

Author: wimglenn

Grammar/python.gram

@@ -642,11 +642,11 @@ star_named_expression[expr_ty]:
     | '*' a=bitwise_or { _PyAST_Starred(a, Load, EXTRA) }
     | named_expression
 
-assigment_expression[expr_ty]:
+assignment_expression[expr_ty]:
     | a=NAME ':=' ~ b=expression { _PyAST_NamedExpr(CHECK(expr_ty, _PyPegen_set_expr_context(p, a, Store)), b, EXTRA) }
 
 named_expression[expr_ty]:
-    | assigment_expression
+    | assignment_expression
     | invalid_named_expression
     | expression !':='
 
@@ -903,7 +903,7 @@ setcomp[expr_ty]:
     | invalid_comprehension
 
 genexp[expr_ty]:
-    | '(' a=( assigment_expression | expression !':=') b=for_if_clauses ')' { _PyAST_GeneratorExp(a, b, EXTRA) }
+    | '(' a=( assignment_expression | expression !':=') b=for_if_clauses ')' { _PyAST_GeneratorExp(a, b, EXTRA) }
     | invalid_comprehension
 
 dictcomp[expr_ty]:
@@ -918,7 +918,7 @@ arguments[expr_ty] (memo):
     | invalid_arguments
 
 args[expr_ty]:
-    | a[asdl_expr_seq*]=','.(starred_expression | ( assigment_expression | expression !':=') !'=')+ b=[',' k=kwargs {k}] {
+    | a[asdl_expr_seq*]=','.(starred_expression | ( assignment_expression | expression !':=') !'=')+ b=[',' k=kwargs {k}] {
         _PyPegen_collect_call_seqs(p, a, b, EXTRA) }
     | a=kwargs { _PyAST_Call(_PyPegen_dummy_name(p),
                           CHECK_NULL_ALLOWED(asdl_expr_seq*, _PyPegen_seq_extract_starred_exprs(p, a)),