chore: remove session pool implementation

Removes the SessionPool and related classes and deprecates the SessionPoolOptions class.
This simplifies large parts of the code, as the only possible code path is the use of
multiplexed sessions.

Author: olavloite

.github/sync-repo-settings.yaml

@@ -14,7 +14,6 @@ branchProtectionRules:
       - units (8)
       - units (11)
       - 'Kokoro - Test: Integration'
-      - 'Kokoro - Test: Integration with Multiplexed Sessions'
       - cla/google
       - checkstyle
       - compile (8)
@@ -154,7 +153,6 @@ branchProtectionRules:
       - units (8)
       - units (11)
       - 'Kokoro - Test: Integration'
-      - 'Kokoro - Test: Integration with Multiplexed Sessions'
       - cla/google
       - checkstyle
       - compile (8)
@@ -173,7 +171,6 @@ branchProtectionRules:
       - units (8)
       - units (11)
       - 'Kokoro - Test: Integration'
-      - 'Kokoro - Test: Integration with Multiplexed Sessions'
       - cla/google
       - checkstyle
       - compile (8)
@@ -194,7 +191,6 @@ branchProtectionRules:
       - units (8)
       - units (11)
       - 'Kokoro - Test: Integration'
-      - 'Kokoro - Test: Integration with Multiplexed Sessions'
       - cla/google
       - checkstyle
       - compile (8)
@@ -215,7 +211,6 @@ branchProtectionRules:
       - units (8)
       - units (11)
       - 'Kokoro - Test: Integration'
-      - 'Kokoro - Test: Integration with Multiplexed Sessions'
       - cla/google
       - checkstyle
       - compile (8)

.kokoro/presubmit/integration-multiplexed-sessions-enabled.cfg

@@ -26,11 +26,6 @@
  */
 abstract class AbstractMultiplexedSessionDatabaseClient implements DatabaseClient {
 
-  @Override
-  public String getDatabaseRole() {
-    throw new UnsupportedOperationException();
-  }
-
   @Override
   public Timestamp writeAtLeastOnce(Iterable<Mutation> mutations) throws SpannerException {
     return writeAtLeastOnceWithOptions(mutations).getCommitTimestamp();