chore: drop empty sonatype credential placeholders from gradle.properties (AIC-2662)

These empty sonatypeUsername/sonatypePassword placeholders aren't needed; the
core SDK module (lib/sdk/server) carries none and publishes fine. The nexus
publish plugin resolves credentials from the environment at release time.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ctawiah

lib/sdk/server-ai/gradle.properties

@@ -1,8 +1,3 @@
 #x-release-please-start-version
 version=0.1.0
 #x-release-please-end
-
-# The following empty ossrh properties are used by LaunchDarkly's internal integration testing framework
-# and should not be needed for typical development purposes (including by third-party developers).
-sonatypeUsername=
-sonatypePassword=