ci: remove patch file for packpack

The packpack-dont-decline-custom-version.patch file was introduced in
9707a7bd (github-ci: support the new version format) and tried to resolve
the issue that actually did not exist. PackPack supports accepting a
custom version (pay attention to `?=`) [1] and the patch is not needed.

[1] https://github.com/packpack/packpack/blob/194f898750cbbee6dd35255fe8aa7ec878eb3836/pack/config.mk#L45

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci

extra/packpack-dont-decline-custom-version.patch

-diff --git a/pack/config.mk b/pack/config.mk
-index 2ceb36d..6f8dfaa 100644
---- a/pack/config.mk
-+++ b/pack/config.mk
-@@ -42,10 +42,12 @@ DESCRIBE := $(shell git describe --long --always)
- # Sic: please follow Semantic Versioning (http://semver.org),
- # Debian policies and Fedora guidelines then planning your releases.
- #
--VERSION ?= $(shell echo $(DESCRIBE) | sed -n 's/^\([0-9\.]*\)-\([0-9]*\)-\([a-z0-9]*\)/\1.\2/p')
-+ifeq ($(VERSION),)
-+VERSION = $(shell echo $(DESCRIBE) | sed -n 's/^\([0-9\.]*\)-\([0-9]*\)-\([a-z0-9]*\)/\1.\2/p')
- ifeq ($(VERSION),) # Fallback
- VERSION := 0.0.1
- endif
-+endif
- 
- # The number of times this version of the software has been packaged.
- # This feature is not implemented yet, therefore value is always set to 1.