Update dcmtk.pc.in

[Cheney-W]

Hello, I'm a member of Microsoft VCPKG. When I install dcmtk by vcpkg after we updated the pkg-config to 1.8.0, I got below error:

Package dcmtk was not found in the pkg-config search path.
Perhaps you should add the directory containing `dcmtk.pc'
to the PKG_CONFIG_PATH environment variable
Package 'dcmtk', required by 'virtual:world', not found

Above error also could be reproduced by command:
pkg-config.exe --print-errors --exists dcmtk --with-path={path of pc file}

This issue occurred because there were leading spaces in the content of the pc file. After removing the spaces, the issue was resolved.

 Name: DCMTK
 Description: DICOM Toolkit (DCMTK)
 URL: https://dcmtk.org
 Version: 3.6.7

To maintain consistent formatting, I removed all the spaces.

[michaelonken]

Merged into local testing branch, will be visible on GitHub master branch within a few days. Thanks for the report and patch!