Move signapk to a dedicated "host" target

Migrate off of one target onto another that should be identical.
"conscrypt" is about to be refactored for on-device use and signapk
needs to be unaffected.

Bug: 113148576
Test: make checkbuild
Change-Id: I3cecb4cc8fb8349383a82c8e430c936651e0835a

tools/signapk/Android.bp

@@ -24,7 +24,7 @@ java_library_host {
         "apksig",
         "bouncycastle-unbundled",
         "bouncycastle-bcpkix-unbundled",
-        "conscrypt",
+        "conscrypt-nojarjar",
     ],
 
     required: ["libconscrypt_openjdk_jni"],