CLN: Deduplicate show_versions
Closes #26814 

The old version had special cases for numpy, scipy, and pytz. All those now provide a standard `__version__`. xlrd and xlwt are the only special ones now (`__version__`)

I messed up the minimum xlwt version in the last PR. I copied openpyxl's rather than xlwt's. That's now fixed.


I prettied up the output format a bit, to align the version numbers. Hope that 's OK.

```
INSTALLED VERSIONS
------------------
commit           : cbc6edf8bfad33c8bc698a3d035b593d921b0112
python           : 3.7.3.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 18.6.0
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 0.25.0.dev0+729.gcbc6edf8b
pytest           : 4.6.2
pip              : 19.1.1
setuptools       : 41.0.1
Cython           : 0.29.10
numpy            : 1.17.0.dev0+5b06588
scipy            : 1.3.0
pyarrow          : 0.13.0
xarray           : 0.12.1
IPython          : 7.5.0
sphinx           : 1.8.5
patsy            : 0.5.1
dateutil         : 2.7.3
pytz             : 2018.5
blosc            : 1.5.1
bottleneck       : 1.2.1
tables           : 3.5.1
numexpr          : 2.6.8
feather          : 0.4.0
matplotlib       : 3.1.0
openpyxl         : 2.5.11
xlrd             : 1.1.0
xlwt             : 1.3.0
xlsxwriter       : 1.1.2
lxml.etree       : 4.2.5
bs4              : 4.7.1
html5lib         : 1.0.1
sqlalchemy       : 1.2.14
pymysql          : 0.9.2
psycopg2         : 2.7.6.1 (dt dec pq3 ext lo64)
jinja2           : 2.10.1
s3fs             : 0.1.6
fastparquet      : None
pandas_gbq       : 0.10.0
pandas_datareader: None
gcsfs            : 0.1.2

```