Cleanup: Remove dead codepath related on rsync step

It was not used for a while, and it's not possible to rsync to the
server.

The reason why rsync step existed is because of upload performance.
But if FileUpload step is really not so much performant it is to be
fixed on Buildbot project side (or re-configured on our side to give
more suitable blocksize).

master.cfg

@@ -182,8 +182,7 @@ c['builders'] = []
 
 # Add builder utility.
 
-def add_builder(c, name, platforms, factory, branch='',
-                rsync=False, hour=3, minute=0):
+def add_builder(c, name, platforms, factory, branch='', hour=3, minute=0):
     for platform in platforms:
         workernames = []
         builder_name = f'{name}_{platform}'
@@ -194,7 +193,7 @@ def add_builder(c, name, platforms, factory, branch='',
                 builder_name = f"{worker['platform_short']}_{name}"
 
         if workernames:
-            f = factory(builder_name, branch, rsync)
+            f = factory(builder_name, branch)
             c['builders'].append(BuilderConfig(name=builder_name,
                                                workernames=workernames,
                                                factory=f,
@@ -225,25 +224,15 @@ def git_step(branch=''):
                          submodules=True)
 
 
-def rsync_step(python_command, id, branch, rsync_script):
-    return ShellCommand(name='rsync',
-                        command=[python_command, rsync_script, id, branch],
-                        description='uploading',
-                        descriptionDone='uploaded',
-                        workdir='install',
-                        haltOnFailure=True)
-
-
 # Generic builder.
 
-def generic_builder(id, branch='', rsync=False):
+def generic_builder(id, branch=''):
     # TODO(sergey): Consider using pathlib.
     filename = f'uploaded/buildbot_upload_{id}.zip'
     update_script = '../blender.git/build_files/buildbot/slave_update.py'
     compile_script = '../blender.git/build_files/buildbot/slave_compile.py'
     test_script = '../blender.git/build_files/buildbot/slave_test.py'
     pack_script = '../blender.git/build_files/buildbot/slave_pack.py'
-    rsync_script = '../blender.git/build_files/buildbot/slave_rsync.py'
     unpack_script = 'master_unpack.py'
 
     # NOTE: On Windows never includes major version in the executable name,
@@ -277,14 +266,11 @@ def generic_builder(id, branch='', rsync=False):
         descriptionDone='packaged',
         haltOnFailure=True))
 
-    if rsync:
-        f.addStep(rsync_step(python_command, id, git_branch, rsync_script))
-    else:
-        f.addStep(FileUpload(name='upload',
-                             workersrc='buildbot_upload.zip',
-                             masterdest=filename,
-                             maxsize=500 * 1024 * 1024,
-                             workdir='install'))
+    f.addStep(FileUpload(name='upload',
+                         workersrc='buildbot_upload.zip',
+                         masterdest=filename,
+                         maxsize=500 * 1024 * 1024,
+                         workdir='install'))
     f.addStep(MasterShellCommand(name='unpack',
                                  command=['python3.7',
                                           unpack_script,