soup: Remove limited fetcher plugin

Besides the relatively recent update to libsoup-3, this has not seen
much development and lacks several features.  There does not seem to be
any advantage over using the curl plugin.  So just remove it to reduce
the maintenance burden.

scripts/test.sh

@@ -272,7 +272,7 @@ all|alpine|codeql|coverage|sonarcloud|no-dbg|no-testable-ke)
 	if [ "$TEST" = "no-testable-ke" ]; then
 		CONFIG="$CONFIG --without-testable-ke"
 	fi
-	DEPS="$DEPS libcurl4-gnutls-dev libsoup-3.0-dev libunbound-dev libldns-dev
+	DEPS="$DEPS libcurl4-gnutls-dev libunbound-dev libldns-dev
 		  libmysqlclient-dev libsqlite3-dev
 		  libldap2-dev libpcsclite-dev libpam0g-dev binutils-dev libnm-dev
 		  libjson-c-dev libtspi-dev libsystemd-dev
@@ -285,7 +285,7 @@ all|alpine|codeql|coverage|sonarcloud|no-dbg|no-testable-ke)
 	fi
 	if [ "$TEST" = "alpine" ]; then
 		# override the whole list for alpine
-		DEPS="git gmp-dev openldap-dev curl-dev ldns-dev unbound-dev libsoup3-dev
+		DEPS="git gmp-dev openldap-dev curl-dev ldns-dev unbound-dev
 			  libxml2-dev tpm2-tss-dev tpm2-tss-sys mariadb-dev wolfssl-dev
 			  botan3-dev pcsc-lite-dev networkmanager-dev
 			  linux-pam-dev iptables-dev libselinux-dev binutils-dev libunwind-dev