[SPARK-32073][R] Drop R < 3.5 support

### What changes were proposed in this pull request?

Spark 3.0 accidentally dropped R < 3.5. It is built by R 3.6.3 which not support R < 3.5:

```
Error in readRDS(pfile) : cannot read workspace version 3 written by R 3.6.3; need R 3.5.0 or newer version.
```

In fact, with SPARK-31918, we will have to drop R < 3.5 entirely to support R 4.0.0. This is inevitable to release on CRAN because they require to make the tests pass with the latest R.

### Why are the changes needed?

To show the supported versions correctly, and support R 4.0.0 to unblock the releases.

### Does this PR introduce _any_ user-facing change?

In fact, no because Spark 3.0.0 already does not work with R < 3.5.
Compared to Spark 2.4, yes. R < 3.5 would not work.

### How was this patch tested?

Jenkins should test it out.

Closes #28908 from HyukjinKwon/SPARK-32073.

Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>

R/WINDOWS.md

@@ -22,8 +22,8 @@ To build SparkR on Windows, the following steps are required
 
 1. Make sure `bash` is available and in `PATH` if you already have a built-in `bash` on Windows. If you do not have, install [Cygwin](https://www.cygwin.com/).
 
-2. Install R (>= 3.1) and [Rtools](https://cloud.r-project.org/bin/windows/Rtools/). Make sure to
-include Rtools and R in `PATH`. Note that support for R prior to version 3.4 is deprecated as of Spark 3.0.0.
+2. Install R (>= 3.5) and [Rtools](https://cloud.r-project.org/bin/windows/Rtools/). Make sure to
+include Rtools and R in `PATH`.
 
 3. Install JDK that SparkR supports (see `R/pkg/DESCRIPTION`), and set `JAVA_HOME` in the system environment variables.
 

R/pkg/DESCRIPTION

@@ -15,7 +15,7 @@ URL: https://www.apache.org/ https://spark.apache.org/
 BugReports: https://spark.apache.org/contributing.html
 SystemRequirements: Java (>= 8, < 12)
 Depends:
-    R (>= 3.1),
+    R (>= 3.5),
     methods
 Suggests:
     knitr,

R/pkg/inst/profile/general.R

@@ -16,10 +16,6 @@
 #
 
 .First <- function() {
-  if (utils::compareVersion(paste0(R.version$major, ".", R.version$minor), "3.4.0") == -1) {
-    warning("Support for R prior to version 3.4 is deprecated since Spark 3.0.0")
-  }
-
   packageDir <- Sys.getenv("SPARKR_PACKAGE_DIR")
   dirs <- strsplit(packageDir, ",")[[1]]
   .libPaths(c(dirs, .libPaths()))

R/pkg/inst/profile/shell.R

@@ -16,10 +16,6 @@
 #
 
 .First <- function() {
-  if (utils::compareVersion(paste0(R.version$major, ".", R.version$minor), "3.4.0") == -1) {
-    warning("Support for R prior to version 3.4 is deprecated since Spark 3.0.0")
-  }
-
   home <- Sys.getenv("SPARK_HOME")
   .libPaths(c(file.path(home, "R", "lib"), .libPaths()))
   Sys.setenv(NOAWT = 1)

docs/index.md

@@ -44,10 +44,9 @@ source, visit [Building Spark](building-spark.html).
 
 Spark runs on both Windows and UNIX-like systems (e.g. Linux, Mac OS), and it should run on any platform that runs a supported version of Java. This should include JVMs on x86_64 and ARM64. It's easy to run locally on one machine --- all you need is to have `java` installed on your system `PATH`, or the `JAVA_HOME` environment variable pointing to a Java installation.
 
-Spark runs on Java 8/11, Scala 2.12, Python 2.7+/3.4+ and R 3.1+.
+Spark runs on Java 8/11, Scala 2.12, Python 2.7+/3.4+ and R 3.5+.
 Java 8 prior to version 8u92 support is deprecated as of Spark 3.0.0.
 Python 2 and Python 3 prior to version 3.6 support is deprecated as of Spark 3.0.0.
-R prior to version 3.4 support is deprecated as of Spark 3.0.0.
 For the Scala API, Spark {{site.SPARK_VERSION}}
 uses Scala {{site.SCALA_BINARY_VERSION}}. You will need to use a compatible Scala version
 ({{site.SCALA_BINARY_VERSION}}.x).