Revert "a3xelte: Try using r15p0 revision of GPU driver"

This reverts commit b32b559e.

Using the r15p0 driver causes a surfaceflinger crashes:

08-13 10:56:02.841 21220 21220 F DEBUG : LineageOS Version: '14.1-20170811-UNOFFICIAL-a3xeltexx'
08-13 10:56:02.841 21220 21220 F DEBUG : Build fingerprint: 'samsung/a3xeltexx/a3xelte:6.0.1/MMB29K/A310FXXU3BQC2:user/release-keys'
08-13 10:56:02.841 21220 21220 F DEBUG : Revision: '0'
08-13 10:56:02.841 21220 21220 F DEBUG : ABI: 'arm'
08-13 10:56:02.841 21220 21220 F DEBUG : pid: 21153, tid: 21181, name: mali-renderer >>> /system/bin/surfaceflinger <<<
08-13 10:56:02.841 21220 21220 F DEBUG : signal 6 (SIGABRT), code -6 (SI_TKILL), fault addr --------
08-13 10:56:02.841 21220 21220 F DEBUG : r0 00000000 r1 000052bd r2 00000006 r3 00000008
08-13 10:56:02.841 21220 21220 F DEBUG : r4 f4309978 r5 00000006 r6 f4309920 r7 0000010c
08-13 10:56:02.841 21220 21220 F DEBUG : r8 00000003 r9 f4d06a00 sl 00000000 fp 00000002
08-13 10:56:02.841 21220 21220 F DEBUG : ip 0000000e sp f43097d0 lr f6c6ed07 pc f6c71564 cpsr 20070010
08-13 10:56:02.846 21220 21220 F DEBUG : 08-13 10:56:02.846 21220 21220 F DEBUG : backtrace:
08-13 10:56:02.847 2189 2189 E : debuggerd: worker process 21220 terminated due to signal 11
08-13 10:56:02.847 2189 2189 E : debuggerd: killing target 21153
08-13 10:56:02.914 2247 2247 I ServiceManager: service 'gpu' died
08-13 10:56:02.914  2247  2247 I ServiceManager: service 'SurfaceFlinger' died