litex_boards: Remove short imports since not really longer useful and mess up Python imports.

We could maybe find a better implementation to avoid messing up imports but not sure it's really useful.
This also enforces consistency in platforms/targets.

litex_boards/__init__.py

@@ -1,83 +0,0 @@
-import os
-import sys
-import glob
-import importlib
-
-# Boards Vendors.
-
-vendors = [
-    "adi",
-    "alinx",
-    "aliexpress",
-    "antmicro",
-    "arduino",
-    "berkeleylab",
-    "colorlight",
-    "decklink",
-    "digilent",
-    "efinix",
-    "enclustra",
-    "gsd",
-    "fairwaves",
-    "hackaday",
-    "kosagi",
-    "krtkl",
-    "lattice",
-    "lambdaconcept",
-    "linsn",
-    "muselab",
-    "myminieye",
-    "numato",
-    "qmtech",
-    "qwertyembedded",
-    "radiona",
-    "rhsresearchllc",
-    "rz",
-    "saanlima",
-    "scarabhardware",
-    "siglent",
-    "sipeed",
-    "seeedstudio",
-    "sqrl",
-    "terasic",
-    "trenz",
-    "tul",
-    "xilinx",
-]
-
-# Get all platforms/targets.
-litex_boards_dir = os.path.dirname(os.path.realpath(__file__))
-platforms        = glob.glob(f"{litex_boards_dir}/platforms/*.py")
-targets          = glob.glob(f"{litex_boards_dir}/targets/*.py")
-
-# For each platform:
-for platform in platforms:
-    platform = os.path.basename(platform)
-    platform = platform.replace(".py", "")
-    # Verify if a Vendor prefix is present in platform name, if so create the short import to
-    # allow the platform to be imported with the full name or short name ex:
-    # from litex_boards.platforms import digilent_arty or
-    # from litex_boards.platforms import arty
-    if platform.split("_")[0] in vendors:
-        short_platform = platform[len(platform.split("_")[0])+1:]
-        p = importlib.import_module(f"litex_boards.platforms.{platform}")
-        vars()[short_platform] = p
-        sys.modules[f"litex_boards.platforms.{short_platform}"] = p
-
-# For each target:
-for target in targets:
-    target = os.path.basename(target)
-    target = target.replace(".py", "")
-    # Verify if a Vendor prefix is present in target name, if so create the short import to
-    # allow the target to be imported with the full name or short name ex:
-    # from litex_boards.targets import digilent_arty or
-    # from litex_boards.targets import arty
-    if target.split("_")[0] in vendors:
-        try:
-            short_target = target[len(target.split("_")[0])+1:]
-            t = importlib.import_module(f"litex_boards.targets.{target}")
-            vars()[short_target] = t
-            sys.modules[f"litex_boards.targets.{short_target}"] = t
-        except ModuleNotFoundError:
-            # Not all dependencies for this target is satisfied. Skip.
-            pass