DejaVuSansMono: Fix monospaced (and remove subdirs)

[why]
The original / upstream version of DejaVuSansMono does not have the
trigrams at codepoint U+2630 - U+2637. These have been added manually
(together with some Powerline glyphs) with commit

    bc1f35949 Updates DejaVu fonts from version 2.33 to 2.37 & adds trigrams (2630 through 2627) (fixes #100)

Unfortunately the newly added glyphs were just copied over from
DejaVuSansCondensed and the width does not match the monospaced width of
DejaVuSansMono: the resulting font is not monospaced anymore (but it
should be, by its name part Mono).

[how]
Take the glyphs again from DejaVuSansCondensed but instead of directly
transferring:
 - export glyphs as svg from Condensed font
 - in the Mono font set the width of the empty target glyphs to 1233
 - import the svgs
 - scale the glyphs X to 75% (100% in Y)
 - center the glyphs within the width

The exact same glyphs have been used for all 4 fonts.

[note]
Also remove the subdir structure as this is the new way to hold the font
files. Remember to clean the patched-fonts/ directory up before release.

Fixes: #1864

Reported-by: @pmadzik
Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

src/unpatched-fonts/DejaVuSansMono/README.md

@@ -5,4 +5,12 @@ Its purpose is to provide a wider range of characters while maintaining the orig
 
 For more information have a look at the upstream website: https://github.com/dejavu-fonts/dejavu-fonts
 
+## Preprocessed Source Font
+
+Since Nerd Fonts 1.0.0 we manually added to the source font the trigrams `U+2630` - `U+2637` (and some Powerline glyphs).
+The glyphs had the wrong width, breaking the monospaced property of the Sans **Mono** font.
+
+This has been fixed (i.e. the width adjusted) after Nerd Fonts 3.4.0 (that release number is yet unknown).
+The Powerline glyphs were dropped in that process.
+
 Version: 2.37