Remove Linux pyfastcopy (#3412)

Fixes #3395

dvc/system.py

@@ -16,15 +16,6 @@ if platform.system() == "Windows":
         speedcopy.patch_copyfile()
     except ImportError:
         pass
-else:
-    import sys
-
-    if sys.version_info < (3, 8):
-        try:
-            # Importing the module monkey-patches shutil.copyfile
-            import pyfastcopy  # noqa: F401
-        except ImportError:
-            pass
 
 
 class System(object):

setup.py

@@ -74,7 +74,7 @@ install_requires = [
     "pywin32>=225; sys_platform == 'win32'",
     "networkx>=2.1,<2.4",
     "pydot>=1.2.4",
-    "speedcopy>=2.0.1",
+    "speedcopy>=2.0.1; sys_platform == 'win32'",
     "flatten_json>=0.1.6",
     "texttable>=0.5.2",
 ]