Remove unnecessary Travis files.

Remove .travis/before-install-linux-{cpp,java,python2,python3}.sh, and
remove some lines from before-install-linux-{javascript,go}.sh.

These contained apt commands for configuring the Mono project's GPG key,
which is not used in any of these builds, and pointless apt-get update
calls.

.travis/before-install-linux-go.sh

@@ -2,7 +2,5 @@
 
 set -euo pipefail
 
-sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
-sudo apt-get update -qq
 eval "$(sudo gimme 1.7.3)"
 ( go version ; go env ) || true

.travis/before-install-linux-javascript.sh

@@ -2,7 +2,6 @@
 
 set -euo pipefail
 
-sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
 sudo apt-get update -qq
 curl -sL https://deb.nodesource.com/setup_0.12 | sudo -E bash -
 sudo apt-get install -qq nodejs

.travis/run-tests-python2.sh

@@ -2,8 +2,10 @@
 
 set -euo pipefail
 
+python --version
+
 mvn -q -Dparallel=methods -DthreadCount=4 -Dtest=python2.* test
 
 cd ../runtime/Python2/tests
 
-python run.py
+python run.py

.travis/run-tests-python3.sh

@@ -2,8 +2,10 @@
 
 set -euo pipefail
 
+python3 --version
+
 mvn -q -Dparallel=methods -DthreadCount=4 -Dtest=python3.* test
 
 cd ../runtime/Python3/test
 
-python3.6 run.py
+python3 run.py