srml-contracts: Apply contract removals immediately (#3417)

* Add ability to destroy a contract in the overlay.

* Don't allow contracts to be destroyed in recursive execution.

* Tests for contract self-destruction.

* Don't allow constructor to exit with insufficient balance.

* Remove dead code.

* Bump node runtime spec version.

substrate/node/runtime/src/lib.rs

@@ -80,8 +80,8 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// and set impl_version to equal spec_version. If only runtime
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
-	spec_version: 148,
-	impl_version: 148,
+	spec_version: 149,
+	impl_version: 149,
 	apis: RUNTIME_API_VERSIONS,
 };