main/postmarketos-base-ui: remove tinydm-x11 subpackage (MR 4837)

This reverts commit 518e62df
"main/postmarketos-base-ui: add tinydm subpackage to pull in xinit (MR 4814)"

aports/tinydm now provides its own -x11 subpackage to do this since
https://gitlab.alpinelinux.org/alpine/aports/-/commit/7df6d02609d42617412267b2ea6609cc9b9e3ef3