You have two options:
Configure Workspace Settings (disable the validation for the current workspace): Go to Window > Preferences > Validation and uncheck the manual and build for: XML Schema Validator, XML Validator
Check enable project specific settings (disable the validation for this project): Right-click on the project, select Properties > Validation and uncheck the manual and build for: XML Schema Validator, XML Validator
Right-click on the project and select Validate to make the errors disappear.