chore(main/apt): drop user agent patch

Why remove the patch:

 termux/termux-exec#24

 These changes in termux-exec would cause apt to send invalid
 installation prefix in user agent.

 This patch is not actual for now and can be removed anyway.

***

Background why the patch was added earlier:

 Its only purpose to generate HTTP user agent string specific for
 environment. This lets us to distinguish on server side whether
 user download packages using official Termux app or derivative
 checking the installation prefix path and disallow downloads
 made by non-Termux projects to reduce egress traffic when needed.

packages/apt/build.sh

@@ -3,6 +3,7 @@ TERMUX_PKG_DESCRIPTION="Front-end for the dpkg package manager"
 TERMUX_PKG_LICENSE="GPL-2.0"
 TERMUX_PKG_MAINTAINER="@termux"
 TERMUX_PKG_VERSION="2.7.7"
+TERMUX_PKG_REVISION=1
 TERMUX_PKG_SRCURL=https://deb.debian.org/debian/pool/main/a/apt/apt_${TERMUX_PKG_VERSION}.tar.xz
 TERMUX_PKG_SHA256=d3b3f3b7014f6e561b86c059b89040d0c742cbabc576593c6efaa0dd7b24de77
 # apt-key requires utilities from coreutils, findutils, gpgv, grep, sed.