docs: remove last browserTarget mention from user-facing docs

Remove browserTarget from precedence explanation in --prerender-target
section (line 278). This was the last remaining mention of browserTarget
in user-facing documentation.

Deprecation policy compliance is now 100%:
- browserTarget: Hidden from all user docs ✓
- noSilent: Hidden from all user docs ✓

Users only see options they should actually use. Deprecated options
remain documented in contributor docs (CLAUDE.md) and schema.json.

Author: JohannesHoppe

README.md

@@ -275,7 +275,7 @@ ng deploy --build-target=test
 
 Specifies the Angular architect target to use for prerendering instead of buildTarget.
 
-**Target Precedence:** If `prerenderTarget` is specified, it takes precedence over both `buildTarget` and `browserTarget`. This option has no effect if `--no-build` is active.
+**Target Precedence:** If `prerenderTarget` is specified, it takes precedence over `buildTarget`. This option has no effect if `--no-build` is active.
 
 #### --no-build <a name="no-build"></a>