Cleanup the explicit timeout value for test methods

After HBASE-19948, no need to add explicit timeout for test methods. But there are some new test methods which used explicit timeout and easy to fail when precommit job run them. One example is https://builds.apache.org/job/PreCommit-HBASE-Build/436/testReport/org.apache.hadoop.hbase.coprocessor/TestMetaTableMetrics/testConcurrentAccess/

See http://hbase.apache.org/book.html#hbase.unittests.timeouts