setup: Drop explicit creation of the build dir in sdist

No need to do that since we'll create it in the top-level code as a
first thing anyway.

Signed-off-by: Erik Skultety <eskultet@redhat.com>

setup.py

@@ -235,8 +235,6 @@ class my_sdist(sdist):
                     f_out.write("    " + line.strip() + "\n")
 
     def run(self):
-        Path("build").mkdir(exist_ok=True)
-
         if Path(".git").exists():
             try:
                 self.gen_rpm_spec()