Exclude csharp from performance test continuous runs. (#26458)

This is a workaround for a breakage introduced by https://github.com/grpc/grpc/pull/22964.

tools/internal_ci/linux/grpc_e2e_performance_gke.sh

@@ -88,8 +88,8 @@ buildConfigs() {
         -o "./loadtest_with_prebuilt_workers_${pool}.yaml"
 }
 
-buildConfigs "${WORKER_POOL_8CORE}" "${BIGQUERY_TABLE_8CORE}" -l c++ -l csharp -l go -l java -l python -l ruby
-buildConfigs "${WORKER_POOL_32CORE}" "${BIGQUERY_TABLE_32CORE}" -l c++ -l csharp -l go -l java
+buildConfigs "${WORKER_POOL_8CORE}" "${BIGQUERY_TABLE_8CORE}" -l c++ -l go -l java -l python -l ruby
+buildConfigs "${WORKER_POOL_32CORE}" "${BIGQUERY_TABLE_32CORE}" -l c++ -l go -l java
 
 # Delete prebuilt images on exit.
 deleteImages() {
@@ -103,7 +103,6 @@ trap deleteImages EXIT
 # Build and push prebuilt images for running tests.
 time ../test-infra/bin/prepare_prebuilt_workers \
     -l "cxx:${GRPC_CORE_GITREF}" \
-    -l "csharp:${GRPC_CORE_GITREF}" \
     -l "go:${GRPC_GO_GITREF}" \
     -l "java:${GRPC_JAVA_GITREF}" \
     -l "python:${GRPC_CORE_GITREF}" \

tools/internal_ci/linux/grpc_e2e_performance_v2.sh

@@ -89,8 +89,8 @@ buildConfigs() {
         -o "./loadtest_with_prebuilt_workers_${pool}.yaml"
 }
 
-buildConfigs "${WORKER_POOL_8CORE}" "${BIGQUERY_TABLE_8CORE}" -l c++ -l csharp -l go -l java -l python -l ruby
-buildConfigs "${WORKER_POOL_32CORE}" "${BIGQUERY_TABLE_32CORE}" -l c++ -l csharp -l go -l java
+buildConfigs "${WORKER_POOL_8CORE}" "${BIGQUERY_TABLE_8CORE}" -l c++ -l go -l java -l python -l ruby
+buildConfigs "${WORKER_POOL_32CORE}" "${BIGQUERY_TABLE_32CORE}" -l c++ -l go -l java
 
 # Delete prebuilt images on exit.
 deleteImages() {
@@ -104,7 +104,6 @@ trap deleteImages EXIT
 # Build and push prebuilt images for running tests.
 time ../test-infra/bin/prepare_prebuilt_workers \
     -l "cxx:${GRPC_CORE_GITREF}" \
-    -l "csharp:${GRPC_CORE_GITREF}" \
     -l "go:${GRPC_GO_GITREF}" \
     -l "java:${GRPC_JAVA_GITREF}" \
     -l "python:${GRPC_CORE_GITREF}" \