pkgbase: Remove runtime dependency on bootloader

It isn't needed and will cause problem when upgrading to a newer release.

Reviewed by:	emaste
MFC after:	2 weeks
Sponsored by:	Beckhoff Automation GmbH & Co. KG
Differential Revision:	https://reviews.freebsd.org/D33878

(cherry picked from commit 5efa7281a7)

release/packages/generate-ucl.sh

@@ -34,6 +34,9 @@ main() {
 	vital="false"
 
 	case "${outname}" in
+		bootloader)
+			pkgdeps=""
+			;;
 		clibs)
 			vital="true"
 			# clibs should not have any dependencies or anything