test: remove redundant code in test

A block of asserts were duplicated in
test/simple/test-child-process-spawn-typeerror.js. This commit
removes the duplicated asserts.

Fixes: https://github.com/joyent/node/pull/8454
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/simple/test-child-process-spawn-typeerror.js

@@ -99,11 +99,5 @@ assert.doesNotThrow(function() { fork(empty, a); });
 assert.doesNotThrow(function() { fork(empty, a, o); });
 assert.doesNotThrow(function() { fork(empty, o); });
 
-// Variants of undefined as explicit 'no argument' at a position
-assert.doesNotThrow(function() { execFile(empty, u, o); });
-assert.doesNotThrow(function() { execFile(empty, a, u); });
-assert.doesNotThrow(function() { execFile(empty, n, o); });
-assert.doesNotThrow(function() { execFile(empty, a, n); });
-
 assert.throws(function() { fork(empty, s); }, TypeError);
 assert.doesNotThrow(function() { fork(empty, a, s); }, TypeError);