[SPARK-34965][BUILD] Remove .sbtopts that duplicately sets the default memory

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

This PR removes `.sbtopts` (added in apache#29286) that duplicately sets the default memory. The default memories are set:

https://github.com/apache/spark/blob/3b634f66c3e4a942178a1e322ae65ce82779625d/build/sbt-launch-lib.bash#L119-L124

### Why are the changes needed?

This file disables the memory option from the `build/sbt` script:

```bash
./build/sbt -mem 6144
```
```
.../jdk-11.0.3.jdk/Contents/Home as default JAVA_HOME.
Note, this will be overridden by -java-home if it is set.
Error occurred during initialization of VM
Initial heap size set to a larger value than the maximum heap size
```

because it adds these memory options at the last:

```bash
/.../bin/java -Xms6144m -Xmx6144m -XX:ReservedCodeCacheSize=256m -Xmx4G -Xss4m -jar build/sbt-launch-1.5.0.jar
```

and Java respects the rightmost memory configurations.

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

No, dev-only.

### How was this patch tested?

Manually ran SBT. It will be tested in the CIs in this Pr.

Closes apache#32062 from HyukjinKwon/SPARK-34965.

Authored-by: HyukjinKwon <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: HyukjinKwon

.sbtopts

@@ -53,6 +53,7 @@ realpath () {
 declare -r noshare_opts="-Dsbt.global.base=project/.sbtboot -Dsbt.boot.directory=project/.boot -Dsbt.ivy.home=project/.ivy"
 declare -r sbt_opts_file=".sbtopts"
 declare -r etc_sbt_opts_file="/etc/sbt/sbtopts"
+declare -r default_sbt_opts="-Xss4m"
 
 usage() {
  cat <<EOM

build/sbt

@@ -17,7 +17,7 @@ declare -a java_args
 declare -a scalac_args
 declare -a sbt_commands
 declare -a maven_profiles
-declare sbt_default_mem=2048
+declare sbt_default_mem=4096
 
 if test -x "$JAVA_HOME/bin/java"; then
     echo -e "Using $JAVA_HOME as default JAVA_HOME."