Delete unnecessary function

when building spark by sbt, the function “runAlternateBoot" in sbt/sbt-launch-lib.bash is not used. And this function is not used by spark code. So I think this function is not necessary. And the option of "sbt.boot.properties" can be configured in the command line when building spark, eg:
sbt/sbt assembly -Dsbt.boot.properties=$bootpropsfile.

The file from https://github.com/sbt/sbt-launcher-package is changed. And the function “runAlternateBoot" is deleted in upstream project. I think spark project should delete this function in file sbt/sbt-launch-lib.bash. Thanks.

Author: KaiXinXiaoLei <huleilei1@huawei.com>

Closes #3224 from KaiXinXiaoLei/deleteFunction and squashes the following commits:

e8eac49 [KaiXinXiaoLei] Delete blank lines.
efe36d4 [KaiXinXiaoLei] Delete unnecessary function

sbt/sbt-launch-lib.bash

@@ -186,10 +186,3 @@ run() {
     "${sbt_commands[@]}" \
     "${residual_args[@]}"
 }
-
-runAlternateBoot() {
-  local bootpropsfile="$1"
-  shift
-  addJava "-Dsbt.boot.properties=$bootpropsfile"
-  run $@
-}