Remove deprecated 'kotlin.js.compiler' property

Only IR compiler available now.

Author: Tapchicoma

integration-test/gradle.properties

@@ -6,7 +6,6 @@ mainKotlinVersion=2.1.0
 mainLibVersion=1.8.0-SNAPSHOT
 
 kotlin.code.style=official
-kotlin.js.compiler=ir
 
 gradle_node_version = 1.2.0
 node_version = 8.9.3