Revert "Added assertion message when ATL is not installed."

This reverts commit c56d4c6c.

Reason for revert: I get the following 13 times per update:

C:/src/trunk/src/build/toolchain/win/setup_toolchain.py:284:
SyntaxWarning: assertion is always true, perhaps remove parentheses?
  assert (vc_lib_atlmfc_path,

Original change's description:
> Added assertion message when ATL is not installed.
> 
> The comment above assert did not match behavior
> of assert. This comment has been fixed and an
> explanatory assertion message was added.
> 
> Bug: None
> Change-Id: If9ac26c578ac45fb9e6dd50b1605ecff13bf1323
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1881161
> Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
> Commit-Queue: Yura Yaroshevich <yura.yaroshevich@gmail.com>
> Cr-Commit-Position: refs/heads/master@{#710425}

TBR=brucedawson@chromium.org,yura.yaroshevich@gmail.com

Change-Id: I18f9431edb7d21435c029a0ce825bfd421f0cc27
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: None
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1888322Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710514}

build/toolchain/win/setup_toolchain.py

@@ -280,10 +280,8 @@ def main():
   assert vc_lib_path
   print('vc_lib_path = ' + gn_helpers.ToGNString(vc_lib_path))
   if (target_store != True):
-    # Path is assumed to exist for desktop applications
-    assert (vc_lib_atlmfc_path,
-            "Microsoft.VisualStudio.Component.VC.ATLMFC is not found, " +
-            "check if it's installed.")
+    # Path is assumed not to exist for desktop applications
+    assert vc_lib_atlmfc_path
   # Possible atlmfc library path gets introduced in the future for store thus
   # output result if a result exists.
   if (vc_lib_atlmfc_path != ''):