meson: Stop using fallback: kwarg for deps that don't need it

Subprojects that use meson.override_dependency() do not require the
caller to provide the dependency variable name inside the subproject.

We also don't want to provide the *subproject* name, because the
subproject name can be `pango-1.50.12` instead of `pango` when using
wrap-file to download the tarball instead of using wrap-git. This
causes the pango subproject to be executed twice when using gtk as
a subproject inside gstreamer (which uses pango-1.50.12 as
a wrap-file).

All the dependencies we use can be switched in this way, but the
remaining ones need to be changed to use meson.override_dependency()
first.

subprojects/fribidi.wrap

@@ -0,0 +1,9 @@
+[wrap-git]
+directory = fribidi
+url = https://github.com/fribidi/fribidi.git
+push-url = git@github.com:fribidi/fribidi.git
+revision = master
+depth = 1
+
+[provide]
+dependency_names = fribidi