[dvsim] PEP8 fixes in dvsim

These should cause no functional change. Detailed list of code changes:

  - Get rid of 'import *': this defeats static analysis tools. Don't
    do it.

  - Add newline after colon in "if foo: bar"

  - Use 'is' to check for equality with boolean literals

  - Don't catch exceptions when running os.system in Deploy.py: the
    os.system function returns the program's exit code.

  - Delete some variables that are written but not read.

  - Minor whitespace changes (missing blank lines between functions;
    weird indentation; missing space after '#')

  - Delete autogenerated module docstrings (they didn't contain any
    information. Maybe it would be good to have a docstring, but at
    the moment it's just noise).

  - Don't use \ as a line continuation character. Use parentheses if
    necessary.

  - Replace code like "foo" + \ "bar" with just "foo" "bar" (Python
    concatenates adjacent string literals just like C). (I didn't do
    this everywhere, but it happened a lot next to the backslash
    continuations, so I got rid of the unnecessary '+' then).

  - Replace "not foo in bar" with "foo not in bar"

  - Use raw strings for regexes with backslashes (r'a\+', not 'a\+')

With these changes, you can run:

  find util/dvsim -name '*.py' | xargs flake8

and see no errors.

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
diff --git a/util/dvsim/dvsim.py b/util/dvsim/dvsim.py
index 39064ab..0cdfc89 100755
--- a/util/dvsim/dvsim.py
+++ b/util/dvsim/dvsim.py
@@ -18,7 +18,6 @@
 import os
 import subprocess
 import sys
-from pathlib import Path
 from signal import SIGINT, signal
 
 import Deploy
@@ -84,6 +83,7 @@
             arg_branch = "default"
     return (arg_branch)
 
+
 # Get the project root directory path - this is used to construct the full paths
 def get_proj_root():
     cmd = ["git", "rev-parse", "--show-toplevel"]