Migrate external_deps prettytable to pypi prettytable (#18661)

Summary:

Migrate `external_deps` `prettytable` to direct pypi dep. Removes tp2 `external_deps` reference and replaces with `fbsource//third-party/pypi/prettytable:prettytable` in `deps`.

Part of the tp2 `external_deps` migration effort (T261267852).

#buildmore
---
*This diff has been authored with assistance from Claude Code*

Differential Revision: D97995123

Author: QuantumManiac

profiler/BUCK

@@ -20,7 +20,9 @@ fbcode_target(_kind = runtime.python_library,
     ],
     base_module = "executorch.profiler",
     visibility = ["PUBLIC"],
-    external_deps = ["prettytable"],
+    deps = [
+        "fbsource//third-party/pypi/prettytable:prettytable",
+    ],
 )
 
 fbcode_target(_kind = runtime.python_library,