package/python-regex: remove outdated comment

python3-regex no longer exists, so there's no need to keep in sync with
it.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/python-regex/python-regex.mk

@@ -4,7 +4,6 @@
 #
 ################################################################################
 
-# Please keep in sync with package/python3-regex/python3-regex.mk
 PYTHON_REGEX_VERSION = 2021.4.4
 PYTHON_REGEX_SOURCE = regex-$(PYTHON_REGEX_VERSION).tar.gz
 PYTHON_REGEX_SITE = https://files.pythonhosted.org/packages/38/3f/4c42a98c9ad7d08c16e7d23b2194a0e4f3b2914662da8bc88986e4e6de1f