linux/pyinstaller: exclude unneeded libraries

Excluding these Linux libraries doesn't seem to cause any side-effects
at runtime (they're also not present in the AppImage).

And the benefit of this, is a reduction of 15 MiB in the final size of
the Linux binary, which should also slightly reduce the app's startup
time (but don't quote me on that). :)

build.spec

@@ -76,6 +76,12 @@ a = Analysis(
     win_private_assemblies=False,
     win_no_prefer_redirects=False,
 )
+# Exclude unneeded Linux libraries
+a.binaries = a.binaries - TOC([
+  ('libicudata.so.66', None, None),
+  ('libicuuc.so.66', None, None),
+  ('librsvg-2.so.2', None, None),
+])
 pyz = PYZ(a.pure, a.zipped_data, cipher=block_cipher)
 exe = EXE(
     pyz,