perf: Move benchmarks to separate gradle build

This patch separates the benchmark Gradle build from the root one.
It allows us to use the latest (built from sources) Gradle
plugin to compile the benchmarks instead of the released one.

build.gradle

@@ -306,12 +306,6 @@ task bundle(type: (isWindows()) ? Zip : Tar) {
     }
 }
 
-task performance {
-    dependsOn 'dist'
-    dependsOn ':performance:build'
-    dependsOn ':performance:run'
-}
-
 task clean {
     doLast {
         file('dist').traverse(type: FileType.ANY, excludeNameFilter: "dependencies", maxDepth: 0) {

performance/build.gradle

@@ -1,9 +1,6 @@
 buildscript {
-    ext.kotlin_version = '+'
-
-    apply from: "$rootDir/gradle/kotlinGradlePlugin.gradle"
-
     repositories {
+        mavenCentral()
         maven {
             url "https://dl.bintray.com/jetbrains/kotlin-native-dependencies"
         }
@@ -20,4 +17,4 @@ konanArtifacts {
     Ring {
         enableOptimization()
     }
-}
+}

performance/settings.gradle

@@ -0,0 +1 @@
+includeBuild '../'

settings.gradle

@@ -27,5 +27,4 @@ include ':backend.native:tests'
 include ':shared'
 include ':tools:helpers'
 include ':tools:kotlin-native-gradle-plugin'
-include ':utilities'
-include ':performance'
+include ':utilities'