Pkgtest: don't include package 'cluster'.

Author: fangerer

com.oracle.truffle.r.test.packages/importantPackages

@@ -16,7 +16,6 @@ caTools,1.17.1,https://cloud.r-project.org/src/contrib/caTools_1.17.1.tar.gz,tru
 cellranger,1.1.0,https://cloud.r-project.org/src/contrib/cellranger_1.1.0.tar.gz,true
 checkmate,1.8.5,https://cloud.r-project.org/src/contrib/checkmate_1.8.5.tar.gz,true
 class,7.3-14,https://cloud.r-project.org/src/contrib/class_7.3-14.tar.gz,true
-cluster,2.0.6,https://cloud.r-project.org/src/contrib/cluster_2.0.6.tar.gz,true
 coda,0.19-1,https://cloud.r-project.org/src/contrib/coda_0.19-1.tar.gz,true
 codetools,0.2-15,https://cloud.r-project.org/src/contrib/codetools_0.2-15.tar.gz,true
 coin,1.2-2,https://cloud.r-project.org/src/contrib/coin_1.2-2.tar.gz,true

com.oracle.truffle.r.test.packages/importantPackagesTop500

@@ -49,7 +49,6 @@ classInt,0.2-3,https://mran.microsoft.com/snapshot/2018-06-20/src/contrib/classI
 cli,1.0.0,https://mran.microsoft.com/snapshot/2018-06-20/src/contrib/cli_1.0.0.tar.gz,false
 clipr,0.4.0,https://mran.microsoft.com/snapshot/2018-06-20/src/contrib/clipr_0.4.0.tar.gz,false
 clisymbols,1.2.0,https://mran.microsoft.com/snapshot/2018-06-20/src/contrib/clisymbols_1.2.0.tar.gz,false
-cluster,2.0.7-1,https://mran.microsoft.com/snapshot/2018-06-20/src/contrib/cluster_2.0.7-1.tar.gz,true
 coda,0.19-1,https://mran.microsoft.com/snapshot/2018-06-20/src/contrib/coda_0.19-1.tar.gz,true
 codetools,0.2-15,https://mran.microsoft.com/snapshot/2018-06-20/src/contrib/codetools_0.2-15.tar.gz,true
 coin,1.2-2,https://mran.microsoft.com/snapshot/2018-06-20/src/contrib/coin_1.2-2.tar.gz,true