cleanup: removes unused kokoro config files (#238)

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Source-Link: googleapis/synthtool@4530cc6

Author: yoshi-automation

.kokoro/continuous/dependencies.cfg

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-trace.git",
-        "sha": "584a0b505002e44083879638ff506d866999f76e"
+        "sha": "51f359154ad0d1ecd9e4b750810b18bae2240a78"
       }
     },
     {
@@ -27,7 +27,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "dd230c816f88d0141fcd0be83498986287220d1b"
+        "sha": "4530cc6ff080ef8aca258c1ec92c4db10a1bbfb4"
       }
     }
   ],
@@ -66,27 +66,16 @@
     ".kokoro/common.cfg",
     ".kokoro/common.sh",
     ".kokoro/continuous/common.cfg",
-    ".kokoro/continuous/dependencies.cfg",
-    ".kokoro/continuous/integration.cfg",
-    ".kokoro/continuous/java11.cfg",
-    ".kokoro/continuous/java7.cfg",
-    ".kokoro/continuous/java8-osx.cfg",
-    ".kokoro/continuous/java8-win.cfg",
     ".kokoro/continuous/java8.cfg",
-    ".kokoro/continuous/lint.cfg",
-    ".kokoro/continuous/propose_release.cfg",
-    ".kokoro/continuous/samples.cfg",
     ".kokoro/dependencies.sh",
     ".kokoro/linkage-monitor.sh",
     ".kokoro/nightly/common.cfg",
-    ".kokoro/nightly/dependencies.cfg",
     ".kokoro/nightly/integration.cfg",
     ".kokoro/nightly/java11.cfg",
     ".kokoro/nightly/java7.cfg",
     ".kokoro/nightly/java8-osx.cfg",
     ".kokoro/nightly/java8-win.cfg",
     ".kokoro/nightly/java8.cfg",
-    ".kokoro/nightly/lint.cfg",
     ".kokoro/nightly/samples.cfg",
     ".kokoro/populate-secrets.sh",
     ".kokoro/presubmit/clirr.cfg",