selftests/powerpc/pmu/ebb: remove fixed_instruction.S

Commit 3752e453

 ("selftests/powerpc: Add tests of PMU EBBs") added
selftest testcases to verify EBB interface. instruction_count_test.c
testcase needs a fixed loop function to count overhead. Instead of using
the thirty_two_instruction_loop() in fixed_instruction_loop.S in ebb
folder, file is linked with thirty_two_instruction_loop() in loop.S from
top folder. Since fixed_instruction_loop.S not used, patch removes the
file.

Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220322045638.10443-1-maddy@linux.ibm.com