s390/entry: remove broken and not needed code

LLVM's integrated assembler reports the following error when compiling
entry.S:

<instantiation>:38:5: error: unknown token in expression
 tm %r8,0x0001 # coming from user space?

The correct instruction would have been tmhh instead of tm.
The current code is doing nothing, since (with gas) it get's
translated to a tm instruction which reads from real address 8, which
again contains always zero, and therefore the conditional code is
never executed.
Note that due to the missing displacement gas translates "%r8" into
"8(%r0)".

Also code inspection reveals that this conditional code is not needed.
Therefore remove it.

Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>