Clean up upgrade tracking files and revert R version requirement

- Remove PLOTLYJS_UPGRADE_LOG.md and PLOTLYJS_UPGRADE_TODO.md from git
  (kept locally via .gitignore)
- Revert R version requirement to >= 3.2.0 (plotly.js upgrade doesn't
  require newer R)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: cpsievert

.Rbuildignore

@@ -23,5 +23,3 @@ abbvie.R
 ^\.github$
 ^\.venv$
 CLAUDE\.md
-PLOTLYJS_UPGRADE_LOG\.md
-PLOTLYJS_UPGRADE_TODO\.md

.gitignore

@@ -20,3 +20,5 @@ travis_debug.R
 .httr-oauth
 tests/testthat/Rplots.pdf
 .venv/
+PLOTLYJS_UPGRADE_LOG.md
+PLOTLYJS_UPGRADE_TODO.md

DESCRIPTION

@@ -23,7 +23,7 @@ Description: Create interactive web graphics from 'ggplot2' graphs and/or a cust
 URL: https://plotly-r.com, https://github.com/plotly/plotly.R, https://plotly.com/r/
 BugReports: https://github.com/plotly/plotly.R/issues
 Depends:
-    R (>= 3.5),
+    R (>= 3.2.0),
     ggplot2 (>= 3.0.0)
 Imports:
     tools,