[JITLink][AArch32] Don't adjust Thumb bit in fixup code; it doesn't contribute to branch ranges

We don't have to set or clear the Thumb bit in relocation fixup values.
It's not part of the branch range and the respective encoding functions
like encodeImmBT4BlT1BlxT2() shift out the least significant bit anyway.

This was a leftover from the initial patch before we switched to store
Thumb state in target-flags with D146641.