Revert "Support dropping tables + make sure upsert has the right storage levels that reflect the cached table storage levels"

This reverts commit 7d91591da503eec947d0757f9140d08d6edb1eff.

Conflicts:
	src/main/scala/shark/SharkEnv.scala
	src/main/scala/shark/memstore2/MemoryMetadataManager.scala
	src/main/scala/shark/parse/SharkDDLSemanticAnalyzer.scala
	src/main/scala/shark/parse/SharkSemanticAnalyzer.scala
	src/main/scala/shark/parse/SharkSemanticAnalyzerFactory.scala
Reverted deletion of SharkDDLSemanticAnalyzer.scala