Remove usage of Gradle plugin for now to fix protocol tests

There's an unknown issue with the Gradle plugin that makes it impossible
to load the smithy-protocol-test-traits when trying to build
smithy-aws-protocol-tests. This commit moves back to manually assembling
JARs and removes the Gradle plugin until we figure out how and why it's
broken.

smithy-aws-protocol-tests/build.gradle.kts

@@ -17,10 +17,6 @@ description = "Defines protocol tests for AWS HTTP protocols."
 extra["displayName"] = "Smithy :: AWS :: Protocol Tests"
 extra["moduleName"] = "software.amazon.smithy.aws.protocoltests"
 
-plugins {
-    id("software.amazon.smithy").version("0.4.2")
-}
-
 dependencies {
     api(project(":smithy-protocol-test-traits"))
     api(project(":smithy-aws-traits"))

smithy-aws-protocol-tests/src/main/resources/META-INF/smithy/manifest

@@ -0,0 +1,36 @@
+json-rpc-1-1/main.json
+query/empty-input-output.smithy
+query/input.smithy
+query/input-lists.smithy
+query/input-maps.smithy
+query/main.smithy
+query/xml-errors.smithy
+query/xml-lists.smithy
+query/xml-maps.smithy
+query/xml-structs.smithy
+rest-json/empty-input-output.smithy
+rest-json/endpoint-host-trait.smithy
+rest-json/errors.smithy
+rest-json/http-headers.smithy
+rest-json/http-labels.smithy
+rest-json/http-payload.smithy
+rest-json/http-prefix-headers.smithy
+rest-json/http-query.smithy
+rest-json/json-lists.smithy
+rest-json/json-maps.smithy
+rest-json/json-structs.smithy
+rest-json/main.smithy
+rest-xml/document-lists.smithy
+rest-xml/document-maps.smithy
+rest-xml/document-structs.smithy
+rest-xml/document-xml-attributes.smithy
+rest-xml/empty-input-output.smithy
+rest-xml/endpoint-host-trait.smithy
+rest-xml/errors.smithy
+rest-xml/http-headers.smithy
+rest-xml/http-labels.smithy
+rest-xml/http-payload.smithy
+rest-xml/http-prefix-headers.smithy
+rest-xml/http-query.smithy
+rest-xml/main.smithy
+shared-types.smithy

smithy-aws-protocol-tests/src/test/java/software/amazon/smithy/aws/protocoltests/ModelTest.java

@@ -0,0 +1,17 @@
+package software.amazon.smithy.aws.protocoltests;
+
+import org.junit.jupiter.api.Test;
+import software.amazon.smithy.model.Model;
+
+/**
+ * TODO: fix gradle plugin and remove this code.
+ */
+public class ModelTest {
+    @Test
+    public void loadsModel() {
+        Model.assembler()
+                .discoverModels()
+                .assemble()
+                .unwrap();
+    }
+}