Remove unused default heap size from distribution expansion variables (#68186)

The default heap size now resides in MachineDependentHeap and is applied
per our auto heap settings logic there vs living in jvm.options. For
this reason we no longer need to fill this in at build time, so we can
ditch these template variables.

distribution/build.gradle

@@ -530,8 +530,6 @@ configure(subprojects.findAll { ['archives', 'packages'].contains(it.name) }) {
  *  <dt>path.env</dt>
  *  <dd>The env file sourced before bin/elasticsearch to set environment
  *    variables. Think /etc/defaults/elasticsearch.</dd>
- *  <dt>heap.min and heap.max</dt>
- *  <dd>Default min and max heap</dd>
  *  <dt>scripts.footer</dt>
  *  <dd>Footer appended to control scripts embedded in the distribution that is
  *    (almost) entirely there for cosmetic reasons.</dd>
@@ -543,7 +541,6 @@ configure(subprojects.findAll { ['archives', 'packages'].contains(it.name) }) {
  */
 subprojects {
   ext.expansionsForDistribution = { distributionType, oss, jdk ->
-    final String defaultHeapSize = "1g"
     final String packagingPathData = "path.data: /var/lib/elasticsearch"
     final String pathLogs = "/var/log/elasticsearch"
     final String packagingPathLogs = "path.logs: ${pathLogs}"
@@ -597,9 +594,6 @@ subprojects {
         'def': 'logs/gc.log'
       ],
 
-      'heap.min': defaultHeapSize,
-      'heap.max': defaultHeapSize,
-
       'heap.dump.path': [
         'deb': "-XX:HeapDumpPath=/var/lib/elasticsearch",
         'rpm': "-XX:HeapDumpPath=/var/lib/elasticsearch",