8249628: Remove EA from JDK 15 version string starting with Initial RC promotion

Reviewed-by: tbell, erikj

Author: Jerry Zhou

make/autoconf/version-numbers

@@ -38,7 +38,7 @@ DEFAULT_VERSION_CLASSFILE_MAJOR=59  # "`$EXPR $DEFAULT_VERSION_FEATURE + 44`"
 DEFAULT_VERSION_CLASSFILE_MINOR=0
 DEFAULT_ACCEPTABLE_BOOT_VERSIONS="14 15"
 DEFAULT_JDK_SOURCE_TARGET_VERSION=15
-DEFAULT_PROMOTED_VERSION_PRE=ea
+DEFAULT_PROMOTED_VERSION_PRE=
 
 LAUNCHER_NAME=openjdk
 PRODUCT_NAME=OpenJDK