Merge .lgtm.yml and lgtm.yml

Although both names are supported, only the first configuration
found is used. Since lgtm.yml has higher precedence, we'll use
that to avoid the risk of future problems.

.lgtm.yml

@@ -1,6 +0,0 @@
-
-extraction:
-  java:
-    index:
-      build_command:
-      - mvn clean test

lgtm.yml

@@ -1,2 +1,8 @@
+extraction:
+  java:
+    index:
+      build_command:
+      - mvn clean test
+
 queries:
   - exclude: java/insecure-cookie