Remove toolchain configuration for Kotlin

Kotlin currently only supports JDK17 language level, which is our
minimum requirement so far.
This commit simplifies the toolchain setup until this is needed again.

See 303e363adf

gradle/toolchains.gradle

@@ -95,57 +95,15 @@ plugins.withType(GroovyPlugin) {
 }
 
 pluginManager.withPlugin("kotlin") {
-	// Configure the Kotlin compiler if the 'mainToolchain' property is defined
-	if (mainToolchainConfigured()) {
-		def mainLanguageVersion = mainToolchainLanguageVersion()
-		// See https://kotlinlang.org/docs/gradle.html#attributes-specific-for-jvm
-		def javaVersion = mainLanguageVersion.toString()
-		kotlin {
-			jvmToolchain {
-				languageVersion.set(mainLanguageVersion)
-			}
-		}
-		compileKotlin {
-			kotlinOptions {
-				jvmTarget = javaVersion
-			}
-		}
-		// Compile the test classes with the same version, 'testToolchain' will override if defined
-		compileTestKotlin {
-			kotlinOptions {
-				jvmTarget = javaVersion
-			}
+	// Fallback to JDK17
+	compileKotlin {
+		kotlinOptions {
+			jvmTarget = '17'
 		}
 	}
-	else {
-		// Fallback to JDK17
-		compileKotlin {
-			kotlinOptions {
-				jvmTarget = '17'
-			}
-		}
-		compileTestKotlin {
-			kotlinOptions {
-				jvmTarget = '17'
-			}
-		}
-	}
-
-	if (testToolchainConfigured()) {
-		def testLanguageVersion = testToolchainLanguageVersion()
-		def compiler = javaToolchains.compilerFor {
-			languageVersion = testLanguageVersion
-		}
-		kotlin {
-			jvmToolchain {
-				languageVersion.set(testLanguageVersion)
-			}
-		}
-		// See https://kotlinlang.org/docs/gradle.html#attributes-specific-for-jvm
-		compileTestKotlin {
-			kotlinOptions {
-				jvmTarget = testLanguageVersion.toString()
-			}
+	compileTestKotlin {
+		kotlinOptions {
+			jvmTarget = '17'
 		}
 	}
 }