Remove unnecessary link-time dependence on xproto.

[greenc-FNAL]

This partially reverts commit 7a3f7d0.

[marcmengel]

We could do this, but we do need xproto to build, so we really should make it
depends_on("xproto", type="build", when="+x")
and not just drop it (?),. I'll let you decide which you prefer.

[greenc-FNAL]

We could do this, but we do need xproto to build, so we really should make it depends_on("xproto", type="build", when="+x") and not just drop it (?),. I'll let you decide which you prefer.

You mean like this?
https://github.com/FNALssi/spack/pull/167/files#diff-3647c57590fe54f56f65c1ca0b69dd8a935fafe9420c91038355ddecd8b170fdR236

[marcmengel]

Yes, thanks!