x11/libei: temporarily drop subpackages

Whole tree builds fail to parse subpackage syntax in *_DEPENDS.

$ poudriere bulk -j 132amd64 -a
[...]
[00:02:31] Error: compute_deps_pkg failed to lookup pkgname for x11/libei~basu processing package xwayland-devel-21.0.99.1.664_1 from x11-servers/xwayland-devel -- Is SUBDIR+=libei missing in x11/Makefile?

$ make index
[...]
make_index: xwayland-devel-21.0.99.1.664_1: no entry for /usr/ports/x11/libei~basu
make_index: xwayland-devel-21.0.99.1.664_1: no entry for /usr/ports/x11/libei~basu

Reported by:	David Wolfskill

This reverts commit 367a4956.