Checkstyle: remove unnecessary properties with default values
Checkstyle: remove unnecessary properties with default values

Several properties in checkstyle.xml are using default values.

According to the Checktyle documentation, these are not required if the 
default value is satisfactory. 

Let's remove these unnecessary properties to improve code quality.

The following are links to the Checkstyle documentation for reference:
SuppressionFilter:
http://checkstyle.sourceforge.net/config_filters.html

CustomImportOrder, AvoidStarImport:
http://checkstyle.sourceforge.net/config_imports.html

ConstantName, StaticVariableName, MemberName:
http://checkstyle.sourceforge.net/config_naming.html

LineLength:
http://checkstyle.sourceforge.net/config_sizes.html

NeedBraces, RightCurly:
http://checkstyle.sourceforge.net/config_blocks.html

Severity:
http://checkstyle.sourceforge.net/config.html
se-edu/addressbook-level3