cleanup: delete old unused files

It looks like we have some files in the source tree that are not used
anymore. So there is no sense to keep them.
Files to be deleted: .appveyor.yml, Jenkinsfile, snapcraft.yaml.

NO_DOC=files removal
NO_TEST=files removal
NO_CHANGELOG=files removal

.gitignore

@@ -146,7 +146,6 @@ obj-*/
 parts/
 prime/
 stage/
-*.snap
 ftp.log
 sftp.log
 ftpscript.txt

Jenkinsfile

-#!groovy
-
-stage('Build'){
-    packpack = new org.tarantool.packpack()
-    node {
-        checkout scm
-        packpack.prepareSources()
-    }
-
-    packpack.packpackBuildMatrix('result')
-}

snapcraft.yaml

-name: tarantool
-version: "2.0~git"
-summary: In-memory database and Lua application server
-description: |
- Tarantool is an in-memory database and Lua application server.
-
-  * A drop-in replacement for Lua 5.1, based on LuaJIT 2.1
-  * Lua packages for non-blocking I/O, fibers and HTTP
-  * Indexes: secondary indexes, range queries, index iterators
-  * Transactions: ACID transactions
-  * Replication: asynchronous master-slave and master-master replication
-  * Query language: server-side scripting and stored procedures
-  * Security: authentication and access control
-
-  This snappy contains only tarantool binary.
-confinement: strict
-
-apps:
-  tarantool:
-    command: tarantool
-
-parts:
-    tarantool:
-        source: .
-        plugin: cmake
-        configflags:
-          - -DCMAKE_BUILD_TYPE=RelWithDebInfo
-          - -DENABLE_DIST=OFF # Disable tarantoolctl, init scripts, etc.
-        build-packages:
-          - cmake
-          - make
-          - g++
-          - git
-          - libreadline-dev
-          - libncurses5-dev
-          - libyaml-dev
-          - libiberty-dev # for backtraces
-          - binutils-dev  # for backtraces
-          - zlib1g-dev    # for backtraces
-          - libssl-dev