Remove leftover in build (elastic/x-pack-elasticsearch#2099)

I had added this to help VersionTests.java identify when it was running
in gradle so it could be sure that it got the real Version information
but even running in gradle doesn't give the real version information
because it runs against a build directory instead of a jar. And the jar
is all that has the version information because the version information
is read from the manifest.

Original commit: elastic/x-pack-elasticsearch@3acbd01433

sql/jdbc/build.gradle

@@ -88,7 +88,3 @@ forbiddenApisTest {
   bundledSignatures -= 'jdk-non-portable'
   bundledSignatures += 'jdk-internal'
 }
-
-test.configure {
-  systemProperty 'tests.version.available', 'true'
-}