Revert "Add E040: $(COMMAND) preferred over COMMAND"

This reverts commit 43ad17be02.

The world is not quite ready for this (it breaks devstack completely).
We should probably have this as a non-failing warning-level (we
currently don't have the concept of warnings v errors).

Change-Id: Ife310e96fecf9fc297259d6e99ea09a5ef938a33

README.rst

@@ -44,5 +44,4 @@ Obsolete and deprecated syntax
 
 Rules to identify obsolete and deprecated syntax that should not be used
 
-- E040: $(COMMAND) preferred over `COMMAND`
 - E041: Usage of $[ for arithmetic is deprecated for $((

bashate/bashate.py

@@ -77,11 +77,6 @@ def check_function_decl(line, report):
                            '"^function name {$"', line)
 
 
-def check_backticks(line, report):
-    if re.search('\`.*`', line):
-        report.print_error('E040: $(COMMAND) preferred over `COMMAND`', line)
-
-
 def starts_multiline(line):
     m = re.search("[^<]<<\s*(?P<token>\w+)", line)
     if m:
@@ -193,7 +188,6 @@ class BashateRun(object):
                 check_for_do(logical_line, report)
                 check_if_then(logical_line, report)
                 check_function_decl(logical_line, report)
-                check_backticks(logical_line, report)
                 check_arithmetic(logical_line, report)
 
                 prev_line = logical_line

bashate/tests/samples/E040_bad.sh

@@ -1,4 +0,0 @@
-#!/bin/bash
-
-# E040
-value=`echo TEST`

bashate/tests/test_bashate.py

@@ -107,12 +107,6 @@ class TestBashateSamples(base.TestCase):
         self.assert_error_found('E011', 3)
         self.assert_error_found('E011', 6)
 
-    def test_sample_E040(self):
-        test_files = ['bashate/tests/samples/E040_bad.sh']
-        self.run.check_files(test_files, False)
-
-        self.assert_error_found('E040', 4)
-
     def test_sample_E041(self):
         test_files = ['bashate/tests/samples/E041_bad.sh']
         self.run.check_files(test_files, False)