[REEF-1643] Remove Maven download from AppVeyor dependencies

JIRA:
  [REEF-1643](https://issues.apache.org/jira/browse/REEF-1643)

Pull request:
  This closes #1158
diff --git a/dev/appveyor-install-dependencies.ps1 b/dev/appveyor-install-dependencies.ps1
index 00c0454..8563de5 100644
--- a/dev/appveyor-install-dependencies.ps1
+++ b/dev/appveyor-install-dependencies.ps1
@@ -25,21 +25,6 @@
     New-Item -ItemType Directory -Force -Path $tools | Out-Null
 }
 
-# ========================== maven
-Push-Location $tools
-
-$mavenVer = "3.3.3"
-appveyor DownloadFile "https://archive.apache.org/dist/maven/maven-3/$mavenVer/binaries/apache-maven-$mavenVer-bin.zip" -FileName "maven.zip"
-
-# extract
-Invoke-Expression "7z.exe x maven.zip" | Out-Null
-
-# add maven to environment variables
-$env:Path += ";$tools\apache-maven-$mavenVer\bin"
-$env:M2_HOME = "$tools\apache-maven-$mavenVer"
-
-Pop-Location
-
 # ========================== protoc
 $protocVer = "2.5.0"
 $protocPath = "$tools\protoc-$protocVer"