mips: remove obsolete selection of CPU_HAS_LOAD_STORE_LR

Commit 18d84e2e ("MIPS: make CPU_HAS_LOAD_STORE_LR opt-out") replaced
the config CPU_HAS_LOAD_STORE_LR by the config with an inverted semantics,
making the "LOAD_STORE_LR" cpu configuration the default.
The ./arch/mips/Kconfig was adjusted accordingly.

Later, commit 65ce6197 ("Revert "MIPS: Remove unused R4300 CPU
support"") reintroduces a select CPU_HAS_LOAD_STORE_LR through its revert
commit, restoring the config CPU_R4300 in ./arch/mips/Kconfig before the
refactoring above.

This select however now refers to a non-existing config and is further
unneeded, as LOAD_STORE_LR is the default now.

Remove the obsolete select for the reintroduced mips R4300 architecture.

This issue is identified with ./scripts/checkkconfigsymbols.py.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>