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
[SPARK-4643] [Build] Remove unneeded staging repositories from build

The old location will return a 404.

Author: Daoyuan Wang <daoyuan.wang@intel.com>

Closes #3504 from adrian-wang/repo and squashes the following commits:

f604e05 [Daoyuan Wang] already in maven central, remove at all
f494fac [Daoyuan Wang] spark staging repo outdated