[MINOR][DOCS] Remove unused images; crush PNGs that could use it for good measure

## What changes were proposed in this pull request? Coincidentally, I discovered that a couple images were unused in `docs/`, and then searched and found more, and then realized some PNGs were pretty big and could be crushed, and before I knew it, had done the same for the ASF site (not committed yet). No functional change at all, just less superfluous image data. ## How was this patch tested? `jekyll serve` Author: Sean Owen <sowen@cloudera.com> Closes #14029 from srowen/RemoveCompressImages.

[MINOR][DOCS] Remove unused images; crush PNGs that could use it for good measure
18fb57f5 · Sean Owen · a539b724 · a539b724 · 18fb57f5 · a539b724
Commit 18fb57f5 authored 8 years ago by Sean Owen
--- a/core/src/main/resources/org/apache/spark/ui/static/spark-logo-77x50px-hd.png
+++ b/core/src/main/resources/org/apache/spark/ui/static/spark-logo-77x50px-hd.png
--- a/docs/img/cluster-overview.png
+++ b/docs/img/cluster-overview.png
--- a/docs/img/edge-cut.png
+++ b/docs/img/edge-cut.png
--- a/docs/img/edge_cut_vs_vertex_cut.png
+++ b/docs/img/edge_cut_vs_vertex_cut.png
--- a/docs/img/graph_parallel.png
+++ b/docs/img/graph_parallel.png
--- a/docs/img/graphx_logo.png
+++ b/docs/img/graphx_logo.png
--- a/docs/img/graphx_performance_comparison.png
+++ b/docs/img/graphx_performance_comparison.png
--- a/docs/img/ml-Pipeline.png
+++ b/docs/img/ml-Pipeline.png
--- a/docs/img/ml-PipelineModel.png
+++ b/docs/img/ml-PipelineModel.png
--- a/docs/img/property_graph.png
+++ b/docs/img/property_graph.png
--- a/docs/img/spark-logo-hd.png
+++ b/docs/img/spark-logo-hd.png
--- a/docs/img/spark-webui-accumulators.png
+++ b/docs/img/spark-webui-accumulators.png
--- a/docs/img/streaming-arch.png
+++ b/docs/img/streaming-arch.png
--- a/docs/img/streaming-dstream-ops.png
+++ b/docs/img/streaming-dstream-ops.png
--- a/docs/img/streaming-dstream-window.png
+++ b/docs/img/streaming-dstream-window.png
--- a/docs/img/streaming-dstream.png
+++ b/docs/img/streaming-dstream.png
--- a/docs/img/streaming-flow.png
+++ b/docs/img/streaming-flow.png
--- a/docs/img/streaming-kinesis-arch.png
+++ b/docs/img/streaming-kinesis-arch.png
--- a/docs/img/structured-streaming-example-model.png
+++ b/docs/img/structured-streaming-example-model.png
--- a/docs/img/structured-streaming-late-data.png
+++ b/docs/img/structured-streaming-late-data.png