Manuals: replace "file name" by "filename"

There are many more instances of "filename" or "filenames" than
of "file name" or "file names".

The winner takes it all!

(From yocto-docs rev: 13ef92bc301166c2e21d2603b2501749248dbe91)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/qa-checks.rst

@@ -539,7 +539,7 @@ Errors and Warnings
    when a recipe has been renamed. However, if that is not the case, the
    message might indicate that a private version of a library is being
    erroneously picked up as the provider for a common library. If that
-   is the case, you should add the library's ``.so`` file name to
+   is the case, you should add the library's ``.so`` filename to
    :term:`PRIVATE_LIBS` in the recipe that provides
    the private version of the library.
 

documentation/ref-manual/variables.rst

@@ -3155,7 +3155,7 @@ system and gives an overview of their function and contents.
          IMAGE_NAME ?= "${IMAGE_BASENAME}-${MACHINE}${IMAGE_VERSION_SUFFIX}"
 
    :term:`IMAGE_NAME_SUFFIX`
-      Suffix used for the image output file name - defaults to ``".rootfs"``
+      Suffix used for the image output filename - defaults to ``".rootfs"``
       to distinguish the image file from other files created during image
       building; however if this suffix is redundant or not desired you can
       clear the value of this variable (set the value to ""). For example,