Revert "Enforce Java 11 source version with JDK17"

This reverts commit 6c3d618538e35e6ca28eadc80eb37c52167db963.

Reason for revert: This breaks the jdk17 build using the correct
toolchain. Change I3cef2772b2 attempted to fix it, but it was not
successful and likely requires a solution in Bazel.

Change-Id: I0238614963693f0ba34d3a63c8dc824004298b21
Release-Notes: skip

tools/BUILD

diff --git a/tools/BUILD b/tools/BUILD
index 6b81871..26db1fa 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -25,7 +25,7 @@
     package_configuration = [
         ":error_prone",
     ],
-    source_version = "11",
+    source_version = "17",
     target_version = "17",
     visibility = ["//visibility:public"],
 )