Replace runTestCase with assert helpers [test/built-ins/Number]

test/built-ins/Number/15.7.3-1.js

test/built-ins/Number/15.7.3-2.js

test/built-ins/Number/15.7.4-1.js

test/built-ins/Number/isInteger/Number.isInteger_Double.js

test/built-ins/Number/isInteger/Number.isInteger_Infinity.js

test/built-ins/Number/isInteger/Number.isInteger_NaN.js

.../built-ins/Number/isInteger/Number.isInteger_NonNumber.js

test/built-ins/Number/isInteger/Number.isInteger_String.js

test/built-ins/Number/isInteger/Number.isInteger_Success.js

test/built-ins/Number/prototype/15.7.3.1-1.js

test/built-ins/Number/prototype/15.7.3.1-2.js