chore: regenerate README (#1314)

This PR was generated using Autosynth. 🌈


<details><summary>Log from Synthtool</summary>

```
2021-07-26 03:36:54,996 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-spanner/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-07-26 03:36:56,212 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

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https://source.cloud.google.com/results/invocations/c155b965-9d63-4034-9e70-33d3e964ac86/targets

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.github/readme/synth.metadata/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-spanner.git",
-        "sha": "b0c5f7f1650339d2d4a7601b948bd044dab165a3"
+        "sha": "b4f0bcff28a7b1560fcda927162129e0b24949ea"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "1563597d28eca099d6411bbc29ecd09314a80746"
+        "sha": "dd05f9d12f134871c9e45282349c9856fbebecdd"
       }
     }
   ]

README.md

@@ -219,8 +219,7 @@ dependency to collect the data and exporter dependency to export to backend.
 
 ## Samples
 
-Samples are in the [`samples/`](https://github.com/googleapis/java-spanner/tree/master/samples) directory. The samples' `README.md`
-has instructions for running the samples.
+Samples are in the [`samples/`](https://github.com/googleapis/java-spanner/tree/master/samples) directory.
 
 | Sample                      | Source Code                       | Try it |
 | --------------------------- | --------------------------------- | ------ |