Bug 6886: (follow-up) replace needless <xsl:choose> with <xsl:if>

Bug 6886: (follow-up) replace needless <xsl:choose> with <xsl:if>

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes all tests and QA script.
Switching SingleBranchMode:

Tested with MARC21 and UNIMARC:
- "Don't allow" - branch is not shown in result list
- "Allow" - branch is shown for available items in result list

Changes are consistent over all 3 MARC flavours.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 5b855c76d07d41eff2873f6e2ba9dc3a43f98d11)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>