Remove native-platform 0.14 usage from the buildSrc

It looks like net.rubygrapefruit:native-platform:0.14 is not in
plugins.gradle.org repository anymore.

And it's not used anyway.

> Task :buildSrc:generateExternalPluginSpecBuilders FAILED

'''
FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':buildSrc:generateExternalPluginSpecBuilders'.
> Could not resolve all files for configuration ':buildSrc:compileClasspath'.
   > Could not find native-platform-0.14.jar (net.rubygrapefruit:native-platform:0.14).
     Searched in the following locations:
         https://cache-redirector.jetbrains.com/plugins.gradle.org/net/rubygrapefruit/native-platform/0.14/native-platform-0.14.jar
'''

Can be reproduced with

```gradle --refresh-dependencies -i tasks -Pkotlin.native.enabled=true```

KTI-986

kotlin-native/tools/performance-server/buildSrc/build.gradle.kts

@@ -2,8 +2,6 @@ import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 import java.util.Properties
 import java.io.FileReader
 
-extra["versions.native-platform"] = "0.14"
-
 buildscript {
     java.util.Properties().also {
         it.load(java.io.FileReader(project.file("../../../../gradle.properties")))

kotlin-native/tools/performance-server/ui/buildSrc/build.gradle.kts

@@ -2,8 +2,6 @@ import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 import java.util.Properties
 import java.io.FileReader
 
-extra["versions.native-platform"] = "0.14"
-
 buildscript {
     java.util.Properties().also {
         it.load(java.io.FileReader(project.file("../../../../../gradle.properties")))