[INTERNAL] m.MenuButton: fix class metadata
[INTERNAL] m.MenuButton: fix class metadata

'Boolean' is not a valid property type, the correct type is 'boolean'.
Furthermore, data binding is not supported for aggregations of
cardinality 0..1 (multiple: false), therefore "bindable" does not make
sense (method bindMenu() already should have logged an error).
 
Change-Id: I4ce468868641fbc927091b52272ad9de4cfb55be

SQCLabs/openui5,nzamani/openui5,SAP/openui5,SAP/openui5,cschuff/openui5,olirogers/openui5,SAP/openui5,SQCLabs/openui5,olirogers/openui5,nzamani/openui5,nzamani/openui5,cschuff/openui5,cschuff/openui5,SAP/openui5,olirogers/openui5,SQCLabs/openui5