Delete "cement" string upon publication of 1.2

[zepumph]

From phetsims/density-buoyancy-common#175. This string was deleted from a common code repo while a version of Density was still using it for translation.

As I write this, I think we will need to wait until Density 1.0 and Density 1.1 are not active PhET-iO releases. It isn't just enough to wait for the new version.