edk2-libc: remove gitmodules file added through accidental commit

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4822

Due to an accidental commit went into edk2-libc while
experimenting with some inner-source repos lead to the addition
of gitmodules file and a submodule. This commit is undoing
this change by removing the gitmodules file and the submodule.

Cc: Rebecca Cran <[email protected]>
Cc: Michael D Kinney <[email protected]>
Cc: Jayaprakash N <[email protected]>
Signed-off-by: Jayaprakash N <[email protected]>
Reviewed-by: Rebecca Cran <[email protected]>