ShareTechMono: Remove fi/fl ligs

[why]
When we crate the hard-monospaced Nerd Font Mono variant the ligs will
be shrunk to 1 cell wide, while the content of the `fi` lig is of course
two cells, ending up in strange overwriting issues.

[how]
Remove the `fl` and `fi` ligatures completely.

Fixes: 1631

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

src/unpatched-fonts/ShareTechMono/config.cfg

@@ -0,0 +1,6 @@
+[Config]
+commandline: --removeligatures
+[Subtables]
+ligatures: [
+    "'liga' Standard Ligatures lookup 5 subtable",
+    "'dlig' Discretionary Ligatures lookup 4 subtable" ]