servo: Merge #10976 - Upgrade mach to 0.6; stop vendoring mach (from frewsxcv:novendor-mach); r=mbrubeck

When I originally rewrote Servo's mach bootstrapping (using virtualenv
w/ requirements.txt in #7103), I didn't specify mach as a requirement
because a new version hadn't been published in a while. Now that 0.6
is out, I asked the mach maintainers to publish a new version on PyPI,
so now we can fetch it like the other Python dependencies.

Fixes https://github.com/servo/servo/issues/10728.

Source-Repo: https://github.com/servo/servo
Source-Revision: e39ed932cb8c67eac98d44d00ed5bf642c026846

servo/python/mach_bootstrap.py

@@ -12,7 +12,6 @@ from distutils.spawn import find_executable
 from pipes import quote
 
 SEARCH_PATHS = [
-    os.path.join("python", "mach"),
     os.path.join("python", "tidy"),
     os.path.join("tests", "wpt"),
     os.path.join("tests", "wpt", "harness"),