Replace dedent calls by dedented strings.

[anntzer]

The strings are so short that just using plain dedented literal strings
is just as readable (if not more) than going through dedent(), and this
change saves a call to a not-so-trivial function.

• I have marked all applicable categories:
  • exception-raising fix
  • visual output fix
  • documentation modification
  • new feature
• If applicable, I have mentioned the relevant/related issue(s)

Less important but also useful:

• I have visited the source website, and in particular
  read the known issues

• I have searched through the issue tracker for duplicates

• I have mentioned version numbers, operating system and
  environment, where applicable:

  import tqdm, sys
  print(tqdm.__version__, sys.version, sys.platform)

  4.37.0 3.7.5 (default, Oct 25 2019, 15:51:11) 
  [GCC 7.3.0] linux
  

[codecov-io]

Codecov Report

Merging #837 into devel will decrease coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##            devel     #837      +/-   ##
==========================================
- Coverage   85.23%   85.17%   -0.06%     
==========================================
  Files          15       15              
  Lines         989      985       -4     
  Branches      173      171       -2     
==========================================
- Hits          843      839       -4     
  Misses        140      140              
  Partials        6        6