Consolidate toolchain definitions

Before this, we end up with the surprising result that targeting java versions upto 11 use the latest runtime but the ones after would use the corresponding one.

Also drops definitions for 14, 15, 16

toolchains/BUILD

diff --git a/toolchains/BUILD b/toolchains/BUILD
index c504589..6d22bc5 100644
--- a/toolchains/BUILD
+++ b/toolchains/BUILD
@@ -257,11 +257,11 @@
     actual = ":toolchain",
 )
 
-RELEASES = (8, 9, 10, 11)
+RELEASES = (8, 9, 10, 11, 17, 21)
 
 [
     default_java_toolchain(
-        name = "toolchain_java%d" % release,
+        name = ("toolchain_java%d" if release <= 11 else "toolchain_jdk_%d") % release,
         configuration = DEFAULT_TOOLCHAIN_CONFIGURATION,
         source_version = "%s" % release,
         target_version = "%s" % release,
@@ -269,51 +269,6 @@
     for release in RELEASES
 ]
 
-# A toolchain that targets java 14.
-default_java_toolchain(
-    name = "toolchain_jdk_14",
-    configuration = dict(),
-    java_runtime = "//toolchains:remotejdk_14",
-    source_version = "14",
-    target_version = "14",
-)
-
-# A toolchain that targets java 15.
-default_java_toolchain(
-    name = "toolchain_jdk_15",
-    configuration = dict(),
-    java_runtime = "//toolchains:remotejdk_15",
-    source_version = "15",
-    target_version = "15",
-)
-
-# A toolchain that targets java 16.
-default_java_toolchain(
-    name = "toolchain_jdk_16",
-    configuration = dict(),
-    java_runtime = "//toolchains:remotejdk_16",
-    source_version = "16",
-    target_version = "16",
-)
-
-# A toolchain that targets java 17.
-default_java_toolchain(
-    name = "toolchain_jdk_17",
-    configuration = dict(),
-    java_runtime = "//toolchains:remotejdk_17",
-    source_version = "17",
-    target_version = "17",
-)
-
-# A toolchain that targets java 21.
-default_java_toolchain(
-    name = "toolchain_jdk_21",
-    configuration = dict(),
-    java_runtime = "//toolchains:remotejdk_21",
-    source_version = "21",
-    target_version = "21",
-)
-
 default_java_toolchain(
     name = "prebuilt_toolchain",
     configuration = PREBUILT_TOOLCHAIN_CONFIGURATION,