Take coroutineContext into account in RedundantSuspendModifierInspection

#KT-22651: Fixed

idea/testData/inspectionsLocal/redundantSuspend/coroutineContext.kt

@@ -0,0 +1,8 @@
+// PROBLEM: none
+// WITH_RUNTIME
+
+import kotlin.coroutines.experimental.coroutineContext
+
+<caret>suspend fun test() {
+    coroutineContext
+}