meson: drop libseccomp and libselinux from libbasic linkage

This means libsystemd.so is without them now. This is important
because countless programs link to libsystemd.so, and do not need
to pull in selinux now. And libselinux.so pulls in libpcre2, so
we trim a nice dependency tree.

I'm not sure why libseccomp was listed there. No code seems to
refer to it.

$ diff -u <(ldd ../systemd/build/libsystemd.so|sed 's/0x.*/0x…/') <(ldd build/libsystemd.so|sed 's/0x.*/0x…/')
@@ -4,11 +4,9 @@
 	libzstd.so.1 => /lib64/libzstd.so.1 (0x…
 	liblz4.so.1 => /lib64/liblz4.so.1 (0x…
 	libcap.so.2 => /lib64/libcap.so.2 (0x…
-	libselinux.so.1 => /lib64/libselinux.so.1 (0x…
 	libgcrypt.so.20 => /lib64/libgcrypt.so.20 (0x…
 	libpthread.so.0 => /lib64/libpthread.so.0 (0x…
 	libc.so.6 => /lib64/libc.so.6 (0x…
 	/lib64/ld-linux-x86-64.so.2 (0x…
-	libpcre2-8.so.0 => /lib64/libpcre2-8.so.0 (0x…
 	libdl.so.2 => /lib64/libdl.so.2 (0x…
 	libgpg-error.so.0 => /lib64/libgpg-error.so.0 (0x…

$ diff -u <(ldd ../systemd/build/libudev.so|sed 's/0x.*/0x…/') <(ldd build/libudev.so|sed 's/0x.*/0x…/')
@@ -1,8 +1,5 @@
 	linux-vdso.so.1 (0x…
 	librt.so.1 => /lib64/librt.so.1 (0x…
-	libselinux.so.1 => /lib64/libselinux.so.1 (0x…
 	libpthread.so.0 => /lib64/libpthread.so.0 (0x…
 	libc.so.6 => /lib64/libc.so.6 (0x…
 	/lib64/ld-linux-x86-64.so.2 (0x…
-	libpcre2-8.so.0 => /lib64/libpcre2-8.so.0 (0x…
-	libdl.so.2 => /lib64/libdl.so.2 (0x…