[sonic-cfggen] remove lazy_re workaround due to many optimizations done (#8226)

lazy_re had an issue when importing sonic-cfggen in another application that
uses re.search(). There is no much improvement of lazy_re today after many 
other good optimization work done for sonic-cfggen. It served as a quick 
temporary solution.

Some quick test for fast-reboot and warm-reboot done on top of 201911 branch:

Fast-reboot: from ASIC reset to ports in up state:
with lazy_re: 18 sec
without lazy_re: 18 sec

Warm-reboot: LAG restoration time:
with lazy_re: 73 sec
without lazy_re: 72 sec

So, there is no real optimization since the number of sonic-cfggen calls is greatly 
reduced in latest SONiC. This means it is time to revert this change.

Signed-off-by: Stepan Blyschak <stepanb@nvidia.com>

src/sonic-config-engine/lazy_re.py

@@ -1,22 +0,0 @@
-# monkey patch re.compile to improve import time of some packages
-
-import re
-
-_orig_re_compile = re.compile
-
-
-def __re_compile(*args, **kwargs):
-    class __LazyReCompile(object):
-        def __init__(self, *args, **kwargs):
-            self.args = args
-            self.kwargs = kwargs
-            self.pattern_obj = None
-
-        def __getattr__(self, name):
-            if self.pattern_obj is None:
-                self.pattern_obj = _orig_re_compile(*self.args, **self.kwargs)
-            return getattr(self.pattern_obj, name)
-    return __LazyReCompile(*args, **kwargs)
-
-re.compile = __re_compile
-

src/sonic-config-engine/setup.py

@@ -40,7 +40,6 @@ else:
 # Common modules for python2 and python3
 py_modules = [
     'config_samples',
-    'lazy_re',
     'minigraph',
     'openconfig_acl',
     'portconfig',

src/sonic-config-engine/sonic-cfggen

@@ -17,15 +17,6 @@ See usage string for detail description for arguments.
 
 from __future__ import print_function
 
-# monkey patch re.compile to do lazy regular expression compilation.
-# This is done to improve import time of jinja2, yaml, natsort modules, because they
-# do many regexp compilation at import time, so it will speed up sonic-cfggen invocations
-# that do not require template generation or yaml loading. sonic-cfggen is used in so many places
-# during system boot up that importing jinja2, yaml, natsort every time
-# without lazy regular expression compilation affect boot up time.
-# FIXME: remove this once sonic-cfggen and templates dependencies are replaced with a faster approach
-import lazy_re
-
 import argparse
 import contextlib
 import jinja2